Ongoing Science

[CJ286]

I like playing the Science version of the game. One problem, though - with a methodical approach I've usually unlocked the whole Science tree by the time I make substantial progress beyond Kerbin's SOI. After that, the game becomes a sandbox, and beyond self-satisfaction and self-set missions, there isn't the payoff to conquering other planets. Yet to get much further without great frustration, you do rather need the majority of the science tree, so I wouldn't suggest slowing down the progress of unlocking. But... what if after the Science tree was unlocked, it was possible to go back and spend more science points to further develop individual nodes or components? That is to say, for increasing levels of science points, it could be possible to apply, say, a 5% positive increase to the stats of a part (or even one particular stat at a time - ISP,  for e.g., or crash tolerance), then spend a higher level of scaled science points for a further 2.5% increase, then 1.25% etc... all the way on up to infinity, but constantly scaling up the cost and down the return, to prevent ridiculously unrealistic results. In this way, however, there would be loads more to spend your post-tree science points on, and there would always be a 'point' and a payoff to scoring more science points across the whole Kerbal system.

One or two new 'science fiction' level parts or nodes might be good, too - e.g. something akin to an 'Epstein Drive' - but priced at an absolutely colossal number of science points, to make it a real long term aspirational 'end-game' objective. Alternatively, what if you could spend science points on the 'gamble' of subsequent research that only might payoff some rare new SF discovery - so you could at least feed your late game science points into some kind of scientific 'one armed bandit'?! 

[MR L A]

Could just use a mod that reduces science income  and stop science mining lol. 

For example I use a mod that reduces science and I do not allow the Science Jr component on manned lander missions 

[Helmetman]

@CJ286  It's not that difficult to go anywhere using all the 90+ science nodes without any frustration, less actually. I mean, those parts get you everywhere, period. I'm not saying this to arrogantly expose myself as a pro which I aint lol. But it's kinda the truth so with some more training you'll go to Eeloo without needing all the science nodes. 

As for your ideas...

ISP is determined by fuel type, exhaust temperature, the actual rocket system (i.e. open/closed cycle) combustion chamber/nozzle among other things. So more ISP from a engine means another engine. Meaning something that looks different rather then be the same engine that has it's stats magically increased by clicking a button. Got that?
As for your idea in general, stat increases on parts up to infinite parameters by throwing bulk science at it? NO! The idea in general is, so so but ok nonetheless if you scrap the infinite part.
We learn a lot in real life to make things sturdier with less weight. Or do things more efficient by optimizing systems. But there are no infinite part parameters to be reached, since this isn't possible in real life also.

You also said increased part parameters could increase crash damage. 
Crash damage of ksp parts is already ridiculously OP. I know ksp isn't real life but it already is quite cartoony in how far one can go. If a real rocket would only fall a few centimeters off from it's anchored launch clamps tear and shear may rip the tank apart causing a RUD greater then ever seen in KSP. In ksp we count in several m/s (but this can be next to nothing like a real rocket if you've build gargantua) So that's the relative comparison basically. However not any tank is supposed to survive the crash loads ksp throws at your ship. If you haven't made something to land on a barge without empty fuel tanks your rocket is essentially constructionally devised to lift something and fail miserably if anything goes the other way. Not take bottom loads of any kind. Or side loads for that matter.  These are things KSP forgives you for if your rocket isn't to heavy even at default part values. Dear lord, don't let me upgrade this any further prayer...

 As for a Sci-Fi part. KSP isn't a game style to have science fictional elements, even if you were to argue it as a unlockable achievement for a scientific endgame.These ideas are better suited for mods. And you can always suggest a Epstein drive on the mod forums and manually configure it to be at the end of the techtree. Eventually your success for obtaining a Epstein drive is far greater by having someone mod it rather then wait for Squad who will never do such a thing anyway.

These and many other things are pretty customizable in KSP so it shouldn't necessarily be stock anyway. I do agree with more career diversity (overhaul) which is also moddable by the way so if you can't wait, don't let yourself be waiting.

I hope this was useful for you.

[linuxgurugamer]

Epstein drive is essentially a rocket with infinite fuel.

then you have the timewarp problem.