Dev and IXC only add about 0.1% more to your profits and it's another coin you have to send to an exchange and then dump for Bitcoin (assuming you only want BTC). I think the uptime and security affording by this pool and others like Bitminter and Elegius exceed the paltry add on of those coins.
Not counting uptime/security (unlikely to be affected), the real issue is extra load on the servers. As you pointed out, DVC+IXC are virtually worthless. I'm not even sure if they're 0.1% actually. Adding extra coins to each pool server means each server will be wasting time accessing the SSDs/RAM for those coins, a few CPU cycles, and some bandwidth every time they get a block. That will at least minimally impact bitcoind performance. How much? I can't say, and nobody else really can either. But it is a non-0 impact, and for how worthless they are, I'm not willing to risk ANY performance for junk coins on BTC Guild.
I'm asking this because I don't know / understand not to be a pain:
Could they were on a physically separate server? With some of the databases I deal with 90%+ of the work is done on the main box 10% is done on other ones. The 10% does not "matter" it's what we term "live irrelevant data". It's for the programmers to use live data / connections to test work, if it all goes boom or lags behind no big deal the main database servers don't even know about it. The front end application servers here (I'm assuming the stratum servers for you) know about it and talk to it at the lowest priority, but if the test back end fails no big deal.
I don't know enough about the stratum protocol to know if that's even possible.
And no, I don't think it's worth the time to mine the other coins, but I do want to understand more.
-Dave