As long as the game file says 100% from the load game screen you should be fine imo. I'm not sure what exactly that entails but I'd imagine you would stop time after getting the final snapshot of the final stage and then return to title screen to check if it is infact 100%
Collecting all of the money to buy the upgrades would probably be tedious and boring. The fastest way to get gold is the second bonus game I think, which will get you between 100-200G per minute (I forget how much exactly). You need about 6000G to buy all of the upgrades.
I am in favor of the category being redefined as something like 'All Snapshots' if you need to buy all the upgrades to reach 100%.
If someone completes a run of All Snapshots, and it doesn't go up to 100% in-game, I'll add an All Snapshots category to make the category more interesting to run
I have completed a casual playthrough of the game collecting all 70 snapshots and buying none of the upgrades. The file select screen treats this as 100%.