Don't worry about it. There'll be another crops up. You tend to find that the ones you miss work out for the best in the end. Dropping on something you're after can be a bit of a patience game, but it's worth the wait.
With regards quick change boxes, simplicity is one thing they have. Changewheels give you far more scope, however. With a box you're limited to what gears are in there. With changewheels, you're merely limited by the ones you own. Even with lathes that have none with them, you don't necessarily need to go original either when replacing them. Provided you have the correct bore, pitch etc., you can use any gear set. It's only if you have an unusual spec. partial set that you might need to buy original gears.
Tooling, as mentioned earlier, is one thing to really pay attention to. The more you can get with a lathe the better, as tooling can end up costing a small fortune even for basic bits. What was my jobber lathe up until recently is one which I bought mainly for the tooling which came with it, for example. That was worth more than what I paid for the lathe, and the tooling came with it because the seller wanted it all out of the way. Same with the last lathe I picked up too. There was some tooling with it, which is rusty as hell, granted, (mind you, so is the lathe
), but again, those few pieces in that box would cost more, even if I bought them second hand, than I paid for the lathe.
The lathe itself you may end up selling and upgrading etc., if or when your needs change, but the tooling can readily be kept and used with your next lathe, provided it can take the size of tooling you have. Getting a good selection of tooling with any machine is definitely the part which will save you money in the long run.
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