Alek, it appears that your question is specific to when the RB carries the ball, when running from Trips. Assuming only that case, I think mojo gives the best advice....meaning that no one really knows how the WRs (and even TEs and other RBs for that matter) influence a running play.
One can speculate, but it is not clear. There is supposed to be (as I recall) some "influence" injected by WRs and others when a play is in their "area" of the field (in this case an outside run). It is unclear how much influence exists and which factors are pertinent to that influence.
Personally, I value BLK from my WRs when I'm using them as blockers. However, STR may be equally or more important. Since it does not appear to "directly affect" the play, I suspect that the influence is so slight that it really does not matter and you should just recruit good receivers, and use your best (or a freshman as mentioned) to play during your running plays.
Another thing to MAYBE consider (and this may be giving the engine too much credit) is what defense you are facing. Is the WR facing a LB? or a CB? If the WR is facing a LB (via a 4-4), maybe STR is more important...if facing a CB (via a Nickel), then perhaps BLK is more important?