And while I've watched my max HR drop from 185 to 181 in the last four years, I've also increase my LT 4bpm in just four months.
... Intense training can actually deminish the body's ability to generate new blood vessels. That's why working a program that starts by building a solid base, then moving into incrimentally more intense workouts as the season progresses will provide the greatest results. Tempo rides are very important, but if you're doing them before 12 weeks of base work, you're won't see the gains you would otherwise see with a solid base first.
Just to illustrate the breadth of opinion on these topics, I have to disagree with some of this. First off, a difference of 4 bpm in HR can be entirely due to external factors and is also well withing the margin of error for monitoring heart rate. I'd place much more faith in your gains in terms of wattage at a given level of lactate.
And as far as I know, there is no documented evidence that intense training will reduce the body's ability to create new blood vessels. This sounds quite a bit like what one coach (Rick Crawford) used to say about "blowing up" capillaries with intensity, something he has since abandoned due to a lack of evidence.
That said, what qualifies as "intense" varies. I work with Max Testa at UC Davis for testing and training programs and Sunday's workout was 3hrs w/ a 30' climb at and just below OBLA (4mmol lactate/l) and 2x 20' intervals on the flats done at 20w below OBLA. This would definitely qualify as intense when compared to many of the old-school Friel, etc devotees. The shorter, super-LT intervals will start coming into play as I get closer to my target races, but I'll do stuff like this year-round.
The bonus is that I get to avoid the drudge of endless hours grinding away on LSD rides!
I train about 12-15 hours/week and my longest rides are 3.5 hrs - relatively easy to fin into a schedule with work, kids, etc. For the OP, many recommend the 2x 20' intervals as a solid way to increase your LT. and don't worry about your maxHR - it's pretty irrelevant. Find your LT via testing, whether in a lab or a series of TT efforts (something like 30' all-out TT effort, take your average HR or preferably wattage for the last 20' as an estimate of your LT. Then use that to set your zones.
So many different opinions on these subjects!