It's not only worth it,,, it's imperative!!! You will hone your skills and learn the tricks faster, easier, cheaper, safer, better, indoor, out of the rain, whenever you have a chance. I'm sure there are more reasons....

I have Reflex XTR and there are several excellent planes to fly 3D, most notable is the Yellow Funtana which can be downloaded from http://www.rc-sim.de along with many other. The standard planes that come with it are only there to give the program a bad rep.
The other simulator choice, and some say better for 3D, is the Aerofly Pro but I have no personal exp. of it (yet).

As far as the UCD I have one with an OS.91 four stroke with a pump. With a 15x4w prop its absolutely perfect, balances right on with the battery aft.
Just mind a few pointers:
*Put CF tubes over the pushrods or switch to 3mm (4-40). The supplied ones will bend.
*Use good quality horns and clevises, the barn-door surfaces are so big, any little loosenes will become big flutter.
*Strengthen the horiz. stab with flying wires or CF spars. It will brake off in 3d moves sooner or later.
*Add some extra right thrust for the "oversize" motors, You'll have it lean to the left in vertical pull up and hovering.
*Reinforce the landing gear attachment. Just make some bumpy landings and it will break clean off,,, easier to fix after you brake it off . They put too little glue on at the factory and the pins don't go all the way through like they should. I broke it in the fourth landing. Metal pins through the bulkheads and block, a good helping of epoxy and glasfiber on the outside and it has stayed.
*Put on a better tailwheel from the beginning, e.g. the Sullivan. you'll be landing it Harrier style before you know it. Mind the weight though.
*If going for a lighter motor you may consider putting the rudder servo in the throttle servo bay and use pull-pull. The rudder servo should be strong and fast.
*Practice throttle control. If you overspeed the surfaces will flutter and kill your servos or rip clean off. With a fine pitch prop it'll fly impressively slow and gracefully.

Most of the above came from other peoples experience and has made my UCD an extremely enjoyable experience.

Happy hovering.