It's not really possible for there to be a bubble at the seed stage -- valuations at that stage are "paper" values because there's zero liquidity. Companies also tend not to stay in the seed stage for long enough to cause an asset bubble; they are either able to acquire follow-on funding (at which point they're no longer a "seed" company) or they aren't and they disappear.
The seed stage is increasingly crowded, but IMO that's a good thing.