Respectfully offered, you're always welcome to experiment on your own synth, but the more you know about the circuits and components, the more you'll avoid frustration.
You're correct in the assumption that there are better parts than in 1981.
But better is a variable term unless implemented correctly.
For example, it's possible to install a really high spec'd op-amp in a unit and wind up with more noise, radio reception, feedback, hum and other undesirable attributes.
A 741 opamp only has 1/2 a volt rise time.
Newer ones might be 30 or more.
Definitely there's faster opamps, but since that type of amp usually features a FET input and is wider bandwidth, it may cause problems when directly substituted.
Most circuits are designed around the constraints or features of specific opamps.
Change a part and the circuit may behave strangely or not at all.
Often things work, the tech puts the unit together, then later an issue is discovered.
One fellow brought me his modded 2600 and it received light dimmer noise very well.
I actually have a variac built into the wall for my shop's tracklights, but was able to reproduce his instrument's problem.
My personal view is that fidelity-wise you may make minor improvements, but none so much as to make the work worth doing when weighed against the risk of damage.
I don't think you'll see much results from using faster regulators or better caps in the unit. At least not vs the cost and risk of an accident.
You *might* see some improvements in noise or offset if key resistors are changed to metal film types.
I'd recommend carefully evaluating the synth you intend on modding first for areas you might consider low grade or compromised.
That is, if you hear hum from the unit, consider better filtering, better grounds and that sort of thing.
If it has a lot of noise even when not playing, you might consider redoing the output stage.
If an envelope amount slider outputs some voltage even when not triggered, you might consider a low offset opamp or installation of an offset trimmer.
Make the mod address the deficit.
If swapping opamps, sockets might help if installed, but be certain that the original amp does not use compensation capacitors. (LM301's do, for example.)
One area you might find useful and with great returns is the installation of a faster, higher input impedance amp in LFO circuits.
By changing the opamp and the timing capacitor, most basic LFOs can go into the audio range.
Simple one vco synths with an LFO modded like this can make a world of new FM sounds and it only takes a few parts.
Please note that without a range switch, an LFO speed control can span a huge range after such a mod.
Accurately adjusting the slider might be difficult.
Hope this helps in some way.