Based on Randall's response "Ain't broke ... don't fix it", I wont open it up (unless someone has strong opinions otherwise).
Apologies, I was being somewhat flippant. I do suggest cleaning and inspection, just not necessarily replacing the brushes. As noted, they last a long time; mine appear to still be original and have outlasted both bearings.
Especially if the car is new to you, pay particular attention to the mounting points. It is very common to find the mounting holes worn oblong from working loose, or even the threads stripped in the extension block for the front mount. It's not too hard to repair these areas if the damage is not too far gone, but if left untreated, eventually the generator ears will break off and necessitate a new generator. I reamed the mounting holes back to round, and inserted sleeves of hard brass tubing (held with Loctite).
When reinstalling the generator, be sure to do the final tightening on the front lower bolt
after having set the belt tension and tightened the upper bolt. It cannot be left loose enough to allow any movement (including adjusting the belt) or it will vibrate loose. Not easy to reach down there with the belt in the way, but it can be done. Also note that the top bolt should be double-nutted. You tighten it into the threads in the generator first, and then tighten a nut up against the other side.
I'm also running 60/55 watt halogens with the stock TR3 generator (which is even smaller than the TR4 version). I would say that it depends on your usage as to how acceptable that is. A lot of short trips with the headlights on, or a lot of winter driving (headlights plus wipers & heater) can cause problems even with the originally supplied 36 watt sealed beam headlights (which I believe are NLA). One of the books even recommends recharging the battery after a winter run, presumably to ensure it has enough charge in it to prevent freezing.