Here's some things to consider:
1) How often can I run the server? If it costs 2c to get in R&D and I can slap a Temujin on it and make 2c every time I run it, it's probably better to just run R&D every turn and keep building up wheel counters for one power access. Seeing a second card (allowing you to skip running R&D next turn) isn't that valuable if it's easy to get into R&D every turn.
2) Can I win? If you know the agenda density of R&D and you have a decent chance of winning by accessing multiple cards, it may be worth spending them now, especially if there's a chance the corp could win soon.
3) Can the corp win? If you've seen biotic in the corp's hand, they need 2 points, and they drew past your R&D lock last turn, then they may be able to win. Using turning wheel counters to win now, or at least snipe the agenda the corp is trying to win with, is better than losing the game with unused counters!
Some other edge cases:
Using wheel counters with a legwork to ensure you see every card in HQ is valuable when you want to make sure you don't miss an agenda in their hand.
Using wheel counters with Leela on R&D or HQ is great when the corp has advanced an agenda that you can't access. Steal an agenda, then bounce their advanced agenda for a big tempo play!