I went after Orion more for fun, and because I thought I was safe enough that I could afford the time to do so, than out of any real necessity. I could have built Omega-V bombers rather than going after Orion, though I would have had a bit slower going of it. The time I wasted going after Orion at least allowed enough miniaturizating techs to come in to make for some quite spiffy bombers.
Usually I get to the end of the tree on a small map because I've been farting around making zoo exhibits rather than just finishing the game. Occasionally there will come a game where I actually need to get most of the way through the tree in order to build up a credible attacking force that is good for taking out more than some laggard AI civilization. One of my most memorable games was playing as Meklar on a medium map. I started out locked in the corner with just 4 fertile planets and no hostile ones, needing range 6 to get anywhere; by the time I could get out of my corner, the other races including a Silicoid had grabbed everything. I was sweating bullets constantly in that game! 4 planets is enough for the Meklar to keep up on a small map, but definitely not on a medium map; if any of the top 3 AIs had decided to take a run at me, I would have been toasty. Fortunately the Humans were closest to me, blocking me off from most of the galaxy, and I was careful to stay on good terms with them. My only other direct neighbor was a Sakkra who was only a little better off than I was, territory-wise, so as soon as I could I started trying to poach his systems. It took a long time to wear them down, but eventually I was successful and grabbed some of their planets, though IIRC one of the big empires did nab a couple as well. That paved the way for me to take on the second-weakest AI, at which point I was finally in a postition where I could compete with the big boys. That was another game where I exhausted the tree legitimately.
Looking forward to your Mrrshan report. Sounds like you might have been trying to make things hard on yourself this time.