If you want challenging, the trick is to find the challenge. I solo'ed the BT run using just a level 11 Bounty Hunter, mercenary spec with Mako healing, and one self-heal spell. I did die twice, but those were tactical errors on bosses that I corrected the next time.
I'm really, really enjoying the fact that I don't need 5, 10, 25 and 40 people to get something done. I solo play 95% of the time, and the other 5%, I bring my roommate or a guild mate along, just for dialog fun and social points. I didn't even know there was a spacebar option...I love BT's dialog and pace, and don't mind sitting though the dialog, but options are nice, so thanks for the info, people :-)
Anyway, bottom line: If you need challenge - challenge yourself :-)