Spending that 'grandfather' ISO for someone in 4star land

Roster link:
https://mpq.gamependium.com/rosters/just_a_genius/

I already got a core team of most of the top tier 4 star maxed. But RNGesus has not been kind to me and I am nowhere near a usable 5 star.

I got ‘grandfathered’ into a SHIELD rank of lvl 59, and after spending a bit of it I have about 400+k left. I like to feel like I am making progress by maxing another 4 star (maybe Quake or Nova?), but a sensible part of me also feels that the value of maxing another 4 star is quite small since I will be using those top tier 4 star most of the time.

The other alternative is to expand my 3 star or 2 star farm by champing more of those. This feels like the boring option to me though, but I have been told that the long term benefits are greater.

My aim is to hopefully be able to float higher and reach 1k/1.3k easily every pvp, but for that I think I need 5 stars, and that is just not happening for me now.

Which way should I go? Max 1 more 4 star or farm 3/2 stars?

On a somewhat unrelated note: I think this is the stage where progress seemingly grinds to a halt and is slow to non-existent, and vets start to get sick of the game and quit? I used to look forward to the 1k pvp reward, now I hardly really need any of them, and the only meaningful prize is the 25CP which only grants me a mere ‘chance’ at some I might want (a 5 star cover).

quote from another thread:

I did quake yesterday and I plan on doing nova (2 yellow short still). I plan on adding pun next, then nova, then maybe peggy if some covers come in. beyond that I’m not sure what i’ll do with the kp, antman, moon knight, GR, carnage, px group.