Well, for that size image to be enlarged to a 20x30 print, the resolution drops to a tad over 100 ppi. That is pretty sparse. On the other hand, the images are nice and wouldn't be viewed very close up and you are not paying full boat for the printing. I'd say go for it.
If you don't like how the big prints look when you get them, I'd recommend paying for smaller enlargements in the 11x14 range. At that smaller size they should look great. But try the larger ones first. You might be surprised and quite happy with the result.