I've done the adjustable bias mod on a few 5150's and 6505's. Adding external pots and test points isn't a huge deal either really but I check bias using plate current draw these days and not cathode (+screen) so I always open the amp to bias anyway.
There are two or three points people make about the cool bias. One is reliability like you said. The second is usually 'crossover distortion', which some say is a contributing factor in the sound of the 5150. This 5150 is biased so cold that it's beyond what would normally be considered 'cool'. It's ice cold! The other thing worth noting which may well be different in your amp since it has EL34's and some other changes I think... is that in the 5150/6505 the Screen Grid resistors are 100ohms. In most amps you see those resistors at 470ohms (for 6L6's) or 1Kohms (EL34's). In actually fact 1K is fine for both, so is 1.5K. Some amps even have 2.2K screen grid resistors. They are there to keep the screen at a lower potential than the plate. 470ohm and 1K are legacy values that every just copies. Bugera have used a value between that in amps that can run 6L6 or EL34 but that is actually just stupid. You may as well use 1K for both. You won't hear a difference. Anyway, the value of those resistors is so low in the 5150 that they don't do a good job and I've seen loads of them fried, which is why it they were the first thing I checked on this amp. Increasing the size of these resistors will increase reliability way more than an ice cold bias. The push on ribbon cables don't help the reliablity issue either. I'm going to try and replace them with something like the cables in to the newer amps. Still push on connectors (not great) but with discrete heavier guage wire rather than flat ribbon.
