Was looking around if there was any mash-ups in the corners of the interwebs, but didn’t see anything. Are mashups a way of looking at design here on the forums?
Gumshoe uses d6 exclusively, but what if spending a point allowed you to step up the die value instead of adding a flat number? Kind of like Savage Worlds. Spend one skill point to raise to D8, up to 4 points to get a D20. You’re looking for thresholds of 4, so the highest die value explodes (except for d20, naturally.)
0 - 3 = Miss, no effect, or “Yes, but”
4 - 7 = Success
8 - 11 = Success with +1
12 - 15 = Success with +2
16 - 20 = Success with +3
This could also work with Investigative abilities, but in which case players do in fact roll dice. The 0 - 3 result is the 0-point spend, so there is still basic information found as per Gumshoe’s conceit. Higher thresholds yeild the 1-point spend/2-point spend results. My table likes working with the limits when dice prompt “negative” results, and they feel active in the scene even if the die value “fails.” Gumshoe of course allows for basic information to always be discovered, but knowing the die result feels like it could prompt further investigation, not derail it, as players then get creative to search in a different way, for example.