I thought mine sounded fine after bringing them up on a variac. I did put a slightly larger cap to ground on the outputs to increase bass output a bit. I have a lot of tube gear and I generally feel that if it is not broke, don't fix it. Having said that, I guess if I was giving it to someone, or had the inclination myself, I would replace the electrolytics at a minimum. This is an extremely easy amp to work on, once it is removed from the deck. Most of the parts you will want to change, resistors or caps are right on the bottom. Some people remove the tape bias tube (mine are out) when running as an amp to lessen load on the power supply.
Absolutely 1 of my favorite amps, single ended class a pentode (6bq5, a great sounding tube).
If you get tired of it, let me know, I am thinking of trying to put together a bi or tri amplified system with a bunch of these optimised for the frequency they reproduce.
Good Luck with them!
PS: I have a Roberts operating manual and some schematics around here somewhere if you need a copy.