Just my thinking. I have an older RM-300 evo ii head that's no longer made and it's really loud. It's overdrive is nice and doesn't sound fake unless you really crank it, which I don't. My ABM is 500 evo iii is plenty loud with an efficient cab. The original owner replaced the tube with and Eden 7025 which made it warmer and less harsh and fizzy. Sounds good to me--and significantly better than the RM-300.
As for more more the more watts aspect. I have yet to ever need huge watts in decades of playing. But I have almost always played with reasonable people who weren't in a volume urinating contest. In fact, I know a guy (not know of), who plays stadiums and sold out shows around the world in an headliner act every one would know. He plays those stadiums with a 45w head and one cab with two drivers and he can hear his amp just fine. And, they use wedges and no IEMs. He does get some in the monitor but he can hear his amp and cab. It can be done. (No intent whatsoever to diss anyone with huge wattage amps.)
All that to say, if you love your head, just add something like an overdrive pedal for a little extra grit. Personally I would not replace an amp I love that does what it's intended with more watts I may not actually need when a simple pedal would do the trick. (But I like new heads as much as anyone.) I'm not a "distortion" person, but do like a bit of OD. I have had a Genzler Four On The Floor for a while and love it. It mimics four classic amps (B-15 through ACC 360), and can go from clean to distortion if wanted. But it's perfect for a healthy touch of overdrive and compression. It's very natural sounding and doesn't sound like someone is playing a buzzsaw.
