I think you'd love a P5 (moreso a 10 or upgraded P5 as the extra power is lovely and you can always drop it back to 5 voices with a couple of button presses if desired)... but I wouldn't let any external pressures be the reason for getting one. I would get one if you hear something in the tone that seems missing from the overall sound you want to achieve.
Eh if I were to get one I might just get the P5 and not the P10 because I don't really associate the P10 with the single keyboard version and the dual manual version had more capabilities than the single, so even if I wanted to replicate Carpenter or Brad Fiedel's Prophet 10 work, I'd be missing something anyway. Was just listening to Rick Wakeman's score for the 80s slasher The Burning...all done on a dual Prophet 10. He was talking on the Blu Ray about how he wished he still had one because he loved it so much.
In fact the only time I think the single keyboard Prophet 10 was used was on Danny Zeitlin score for the 70s Invasion Of The Body Snatchers remake (Mostly doing weird warbles and gurgles) and Dan Wyman's scores for Without Warning and Hell Night (which played alongside an orchestra, mostly doing drones and pads)
You always write such weird takes on synths... you do realise the NEW rev 4 Prophet 10 has very little in common with either iteration of the vintage Prophet 10? In so much as any short-comings of the old single keybed P10 do not apply to the rev 4 P10. And the 'extras' on the Dual manual P10 are just different, not better, and certainly a lot uglier and overblown (I mean that thing looks like an organ with the dual manuals).
I say this because you say you'd get the P5 rev 4 over the P10.. but some of the best features of the Rev 4 are ONLY or BEST useful on the P10... high poly in round robin sounds gorgeous (P5 will have note stealing), but moreso the poly unison mode which sounds better than the old P5 did and is basically useless on the new P5 due to low poly, but on P10 you're back to 5 voice in stacked mode but with some VERY interesting layering choices... not just simply mashing two voices together, it's esp prominent with different portament and velocity/aftertouch settings between layered voices. I don't think of P10 in stacked mode as a mere 2 sounds at once, they are ONE sound... designed with essentially 4 oscs, choice of 2 diff filters and differing 'vintage' settings... you can get some REALLY interesting stuff out of the rev 4 P10 you'd never have gotten out of the old P10 or P5... the velocity to filter expression is just the icing on the cake and blows away vintage prophets for atmosphere and beauty.
I think the rev 4 engine is now so good and so flexible, moreso than the old prophets, to the point that 5 voices seems a waste... all that power and not enough poly to express it, that is why the Prophet 10 is THE best prophet ever (Rev 4).
I'm not sure wtf you should care what someone from 40 years ago associates with more or why when it comes to buying a modern synth, unless you're getting an actual dual manual prophet 10 then the sane and BEST buy is the new Prophet 10. The prophet 5 rev 4 is a ridiculous handicap for such new layering and poly unison power... and ftr nobody gives AF about the P5 badge since rev 4 release... the P10 is now the 'Daddy' and unless you own a battered old vintage P5 neither of the new ones have any kudos beyond their respective NEW powers... and there, the P10 owns everything... inc the OB-X8 with it's too low 8 voices (4 stacked), weaker VCOs, and less direct/convoluted layout with menu diving.