Please tell me what parts I should change on my Scalpel to "make it a fair bit lighter" without sacrificing performance, and adding cost. I really look forward to this answer.
In my view, I can only change the wheel set (-200g), the crankset (-150g) and the brakes (-100g), but all will be much more expensive, and also affect durability and performance. ( I doubt the Ax-Lightness clinchers at 305g is stronger and stiffer than my rims at 390g)
It sounds like you were offended by my post which wasn't my intention and honestly, I'm sure your bike works extremely well with that build. It looks like you're missing bar plugs which I'd add (I often use tape, just like you) and then the only thing I'd change would be the pedals. There are sections of trail here that can't really be ridden and walking them in road cleats/shoes would range from being hard to impossible depending on the weather. All really I meant before is that if you're being completely ruthless, there are lighter ways to build a FS 29er without majorly compromising the usability or blowing out the price.
You've said it yourself, there are savings with your wheels, cranks and brakes. Sure you could spend heaps of money to loose grams on those items, but that's not a given if you were starting from scratch.
There are lighter rims than what you're using - even cheap Chinese carbon, let alone if you did spend more money or use tubulars. The money saved using Lasers instead of bladed spokes goes a fair way in making up for using Extralite hubs instead of Tune for example.
If you hunt them down, SWorks cranks can be had for only a bit more than what you're using now and save considerable weight. Even keeping your cranks, weight could be saved with a spiderless chainring.
R1's are another simple weight saving.
You could save weight on your pedals.
On a budget and starting from scratch, there are better options than a Scalpel 29er frame IMO. Frames that are either slightly lighter in the same price bracket or of similar weights but at much lower prices. An extreme example is that some of the open mold weights are comparable in weight and that would let someone spend heaps more of a budget on other items. Also, there are lighter forks than a Lefty too (even ignoring something like a WR with toothpick
sized stanchions). Unless you're getting a Lefty on a stock bike, they aren't cheap.
If you want a light fs, consider buying a 26er Scalpel frame, and use 650b wheels.
If you're a smaller rider, this option, or even an older Spark with 650B wheels seem like fantastic options. It's a shame really that the Scalpel 29er isn't an upsized version of the old bike.