Can the Sky Biome be generated randomly or via research/scrambling/deconstruction? And does it spawn a single enderdragon? It is the biome in the End, after all, and it did spawn a dragon when a first (and last) used it in Mystcraft in MC 1.2.5 or so.
Also, do the bosses in your epic battle dimension continually respawn, or do you have to explore to find more? Kinda wondering if it's remotely possible to have a safe location to drop a matter receiver in a dimension filled with dragons that destroy everything they touch.
Idea: This goes along with the "natural" matter receiver idea I had a while back. What if the RFTools dimensions generate with a modified receiver that (a) only functions in the dimension it generated in, (b) draws power from the dimension itself (or your phased field generator thingy?), and (c) is wither- and dragon-proof, and therefore (d) can only be picked up with a wrench? That way, you don't need to worry about the withers and dragons and whatnot destroying your only way into the dimension, although you'd still need to protect the return transmitter somehow (like in your inventory).
Oh, and by the way (since I haven't gotten around to updating RFTools AGAIN to test this), does the phased field thingy protect you from death by unpowered teleporter as well as by unpowered dimension?