I think the bigger issue is more the stability and age of the tank. The tank is looking good, and going in the right direction. I looked at the tank shots you posted. That anemone isn't looking any better, though, and I'm not sure that tossing a clam in there would be fair to the clam. They seem to like REALLY stable tanks, and frankly at least part of that comes with age.
Eric Borneman wrote a really good article (or thread, I can't remember) about why tanks take about a year, year and a half to really stabilize. Obviously some corals do well in tanks before then, but many mysterious deaths to livestock occur also. He was pointing out that even though most of the live rock die-off and cycle happens fairly quickly, there are often small colonies of sponges, tunicates, and other little things that don't die off immediately. Many will die off over time, which along with the toxic soup that stressed corals emit, can leave the tank water pretty unsafe for delicate organisms. Combine this with learning good habits, frequent water changes, keeping parameters stable, etc. that is just part of being a new hobbyist, is why people are advising to keep some of the easier corals. And, as I see from your photos, you've found some really nice ones.
Anyway, don't shoot yourself in the foot, or add something with needs that would be really hard to meet. Another way of looking at it is would you like a tank that's fairly stable and that you can enjoy or do you want to always be on the knife's edge of a tank crash. A dying clam (or anemone) can wipe out a whole tank, especially a smaller one. Play it safe and enjoy the hobby!
Josh