Brown and sanders may not be as fast as Wallace but I will contend that they may use their speed more effectively because of better route running. I always liked Wallace (until he started to play the fool) but I have also always said he may be our third best best WR in terms of overall talent behind Brown and Sanders.
Also don't underestimate Cotchery. He is one of those WRs that will drive a defense crazy because he always finds the open spot and is available. We will be fine without Wallace. Maybe less ESPN highlight clips but overall effectiveness is what matters and I trust Haley will call a much more effective game than Arians' vertical passing attack that always looked deep.