I think if you're going to use the analog I/O then the extra $ for the XT20 is well worth it. I use 2 LX20s, but use the digital I/O exclusively. While there are, of course, differences in the digital I/O between the two units ... this is been a good choice for my needs. On the other hand ... I've also had my share of transport problems which I'm not sure I would have had if I had gotten XT20s ... but to repair that problem cost me around $100 total ... so it hasn't been too bad yet.
I think taking the extra $ and sinking it into a decent digital board (if you like those) is a good option. My opinion, of course.