First of all, how you acquire tickets rarely affects the chances of sitting together. You should be able to get seats together, whether paying, using miles, or a combo (unless all that's available are scattered middle seats).

Second, most folks here would probably say that $300 is not a very effective use of 25K miles. But that depends a lot on your own travel patterns. If you don't fly internationally, and your domestic flights tend to be short and over weekends anyway, then you may as well use miles. Especially if an extra $50 will get you into F.

Finally, have you looked into leveraging the new alliance to use your miles to fly into DRO? DRO is served by Continental; this page implies that starting July 15, you can redeem DL miles for CO flights. If that works, that would be my choice, since it's a MUCH shorter drive.

http://www.delta.com/skymiles/getmil...dex.jsp#redeem

Have a great trip.