-Unless your bike is made out of Easton-branded Scandium or some of the super-exoctic and now out of production Deda or Columbus stuff feel free to powdercoat away.
-A frame needs to be made with large enough vent holes to clear out the ano solution when it's dunked
-A certain weld rod(5356) takes on coloration better than other weld rods.
-The welds on a 7005 frame will be darker than the seemless looking tube to weld transition you get with a 6061 frame.
-Re-anodizing a 7005 frame might not get you results you are happy with- you will probabally have some spots that are darker than other spots, because you really(really) need to polish 7005 tubes completely before you weld them to get off the first few microns of surface corrosion. The surface finish on any frame must be consistent otherwise the result will be noticeable.
-Very few anodization shops can handle bicycle frames. If something doesn't fit in a 40 gallon drum it's unlikely that most shops can handle it. The ones that can are probabally pretty high end and probably not even be setup to deal with end users.
-Anodizing is, at the level a consumer has it done, hand-made, labor intensive process. Results vary based on the dude who's dunking the frame, what flavor donuts he likes and what's on the radio at the time.
I love ano. It's simple, inexpensive when done in large batches and pretty darn durable. There is a balancing point between a durable ano job that won't scratch(deeper penetration) and a thinner job that scratches easily. An inexperienced anodizer may be afraid to find that middle ground. If you etch in too much you can end up with creaky interfaces.
Powdercoated frames must be media blasted and solvent dipped before they are powdered otherwise the results may vary.
Powdercoat is, in my opinion the most wonderfull way to add pigment to any metal object. The weight gain on ano varies widely based on the type of powdercoat you use, and there are all sorts of powder colors, textures, surface finishes levels of reflectance etc/etc. 40grams for paint so thin you might as well leave it off for 100+gms for a 3d surface texture(rust is one of my personal favorites). It is extremely hard to do multi-color powdercoat jobs that look decent and a shop that doesn't have a good baking process and a clean spray booth may leave you with dust spots or drips.
Phenomenally expensive. The heaviest option. The cost of the paint job is higher than the cost of materials for the frameset or even the manufactured cost of a production frame(foreign or domestic in origin) if we're talking about steel or aluminum.
To do it well takes skill, practice and a lot of expensive equipment and to do it to a standard where it's safe for the health of the painter, let alone the environment, is staggeringly expensive - as a result you get something that looks slightly shinier than powdercoat but isn't as durable and costs 4 times as much.
It's the only way to do really cool stripes and panels and whatnot, but the pricing is just out of this world expensive, and it's the heaviest option. It's really expensive too, did I mention that? You can't powdercoat a carbon fork to match a frame so wet paint is the only option for forks.
What I do with my personal aluminum bikes(as in the ones that I personally get to keep and ride) is take them out of the oven and put parts on them. With 6000 series alloys after the initial surface corrosion the material can and will not corrode any more. Washing your bike is all you need to do. 7000 series aluminum frames are more sucesptible to corrosion, but paininting won't fix that- salt makes little bits of the material precipitate off. You'll see that on some 15 year old mtb frames with riveted on cable stops that there is paint flaking. On powdercoated frames that weren't properly media blasted you'll also see some aluminum-dust related flaking. I have 17 year old 7005 frames that have never been painted. I make sure to wash them and occasionally hit them with some polish, not to get them shiny per se but because when you polish the frame it "seals" the surface finish from corrosion and helps to prevent pitting. It's just a bike frame, not a work of art, and to me, personally I can't justify the extra money for something that is technically unnecessary. I leave my steel frames unpainted and wipe them down with wd40, so I might take it too far.
If you live by the beach, 6000-series aluminum is the best way to go unless you have the will to maintain your frame almost as much as you would a steel bike.
You can hand polish bikes too, hotrod style. I do it for some of my team bikes. It is A LOT of work. A professional mirror polish job is about $600. You can take a mirrior polished frame and have it anodized and it will stay shiny indefinitely. Budget about $800 to have a mirrored clear anodized bike.
The ultimate finish for any aluminum structure is ball-burnishing. That just doesn't make things shiny, it also increases the hardness of the material and relieves a significant amount of stress. In fact we could reduce the wall thickness on our tubing by a wee fair bit if we could ball-burnish, it's that great of a finishing process. Throw some ano on top of that and beadblast in some logos and you have a pretty killer machine with a durable surface finish that weighs nearly nothing that will last forever.
You don't see very many ball-burnished bikes any more. You need a giant burnishing machine to begin with and then you need to build a cage to put inside of the machine that secures the frames in a way so that they can't get damaged. Then you need to build cages of each frame, it all ends up looking like a Ferris wheel. To do that on a production scale you are looking at something about the size of 2 short intermodal shipping containers side by side, a very strong agitator motor, a motor to rotate the spit and hundreds of thousands of small perfectly round bearings, not to mention a few hundred gallons of slurry fluid.
I'm that skinny guy who runs Spooky Bikes