Keeping a few extra dollars was my thought too. The 20 has features that I would LIKE to have, but don't really need. I do fine without them. The infared transfer would have been cool, but I haven't had a time yet when I would have used it. As for the SD card, I don't plan to add any maps to my unit and I can fit 2000 Geocaches which is plenty for me!
Good choice with the Dakota 10! And don't forget, if anything happens to it, it is covered under a year warranty. And don't forget to update the software! Have fun out there!