@rodeo i am in the exact same situation as you. i had an eris and had a ton of problems with it. i was able to switch to the moto droid and i too am eligible for the 30 day return and was considering the switch to the droid x. keep in mind, verizon charges a 35.00 restocking fee, on top of the difference in cost.
for my situation i am going to agree with OMJ. while the droid x may be a better phone now, by the end of the year there are going to be phones that blow that out of the water. i think your wife will be happy in the performance difference just between the stock droid coming from the eris. i was totally surprised its like night and day.
anyway that's just my .02
for me...its the droid until the 4g phones come out