You'll likely get a lower valuation from Foundry than you would from valley or NY firms. But they're worth it. Hope to have them invest in one of my companies someday. Those guys are awesome.
The simple way around that - if you still want Foundry - is to get multiple term sheets and play them off each other. VC firms are like the Blue Angels - they'll follow each other into the ground if one of them leads them that way.