Here are my irrelevant opinions, I'll keep it short:
Combo: score v1 is fine, Shoegazer's suggestion might make it very slightly better than that.
Accuracy: same as above
LN timings: should be made more lenient than score v1, not tighter. There's a reason LN spam maps are made lower OD by mappers.
Mod multipliers: the only thing actually worth adding, finding the right multiplier for each mod so that pp for mods can be added until per-mod leaderboards get implemented.
EDIT: and yeah visual mods shouldn't have multipliers but that's already sorted.
My verdict: score v1 is probably the smallest of problems in osu!mania, other than adding mod multipliers for DT pp this is a waste of time.
Combo: score v1 is fine, Shoegazer's suggestion might make it very slightly better than that.
Accuracy: same as above
LN timings: should be made more lenient than score v1, not tighter. There's a reason LN spam maps are made lower OD by mappers.
Mod multipliers: the only thing actually worth adding, finding the right multiplier for each mod so that pp for mods can be added until per-mod leaderboards get implemented.
EDIT: and yeah visual mods shouldn't have multipliers but that's already sorted.
My verdict: score v1 is probably the smallest of problems in osu!mania, other than adding mod multipliers for DT pp this is a waste of time.