Please forgive me if I missed something simple, but:
do leftover buy points "rollover" to the next buying opportunity.
I cant find anything in forums or the rules that's clear on the point ... and I hope I didnt miss something obvious (but I fear I may have).
Yes and no, depending on what you mean by the next buying opportunity.
Your points can be used to make multiple purchases during a single buy round. For example, if you have 9 points in your hand you can purchase a 4 point card, flip a new card into its spot, and then purchase a 5 point card.
However, your points don't carry over into the next game's buy round. In the previous example, if you bought two 4 point cards, the 1 point leftover point would be lost when you drew your new hand for the next game.