(Thanks. Just got home from the airport. It's been a long day but I'm coming tonight.. will I see you there?)
Sorry, there's nothing wrong with the idea. What's one person's panacea is another person's ho-hum. I like the SPS but they also aggravate me to no end, which obviously influences where I take my tanks. But others will take theirs in other directions. It's all good.
These days my finances influence what I can do with my tanks.
So gone are the days I had 4 reef tanks going. Two (and a planted FW) is quite enough and in some ways even possibly beyond really what I'm capable of. The point I'm sort of randomly stumbling towards here is that I've noticed smaller tanks are not my forte. A bigger tank I can keep stable much easier than a smaller tank. So one thing to take into account when you're thinking of "toy tanks on the side" is that if you go smaller volumes, yes they're cheaper, but they are also less forgiving.
Which sort of leads me to the other random stumbling towards goal and that's of economization of scale by consolidating into a common system. A "frag growout" tank is the same idea for the most part, and then you are tieing into the same parameters, equipment, etc. and thus you can afford bigger things for the one system.
Anyhow those are only one person's considerations though and everyone is different. Sometimes it makes sense to run disparate systems, sometimes it makes sense to consolidate.