Mystcraft consumes too much memory, is unbalanced, and leads to memory leaks.
This is where I have to disagree
If you configure everything correctly, your first and last problems are pretty much non-issues. If nobody can make ages except you, there's no problem, as 40 different ages won't crop up randomly (in which they will unless you configure it).
For the second, by configuring it, you can make everything perfectly balanced. Don't like dense ores? No dense ores! Make everything exactly like the overworld if you want to!! If it were up to me, I'd have the overworld and an age exactly like it, and have the age reset every few weeks, so big holes aren't in the nice "building" age. I'd strongly push the players from auto mining in the overworld, but if they go caving or something, the overworld won't be ruined by big holes from quarries, frame or not.
Also, I vote nay for the server reset, because all the mods are gonna update (well, maybe not soul shards, but it can easily be added in). Though the additions are cool and I can't wait for stuff mainly found in MFR, I'd much rather wait because I am extremely frustrated with all kinds of server play. No offense to you, Jerome, but I just don't like being reset. Fine, ban EE3. I like it, but I'll deal. I'm much less inclined to deal with Xeno's, because it's a cool mod with one thing you don't like. Unfortunately, no configs, and it's your server, and you've done things that make up for it (like letting us vote and listening to my suggestions when I have them). The reason I'm frustrated, though, is resets. I haven't gotten a matter fab yet. Never got to auto mine. And I've been playing FTB for 5 months! I have several hundred posts and likes, and know more about gregtech, thaumcraft, and bees than the average Joe, but I haven't even gotten to them! I got to unweary, pure luck but with terrible traits I can't tell you because I didn't make a beelizer, I haven't gotten a chance to research anything in TC (I made a Thaumicon and a table ;P), and in GT, I haven't gotten UU!
So I hope there's no reset, and I hope I dispelled any Mystcraft Mythcrafts (uh oh, trying too hard on my jokes!)