Sclerotherapy has a very high satisfaction rate as you might judge from its sitting pretty close to the top of the poll on this site.
Your physician is correct as the small vessels can be very difficult to eradicate. The more times sclero is done the harder it is to get rid of the remaining vessels. I thought that was just me until I went to a meeting and that was pretty much the universal feeling of all the participants. The vessels may develop some sort of resistance. Also, logically we try to knock off the larger and more obvious ones first. Finally, there is a matting effect. That means that sometimes when a vessel is successfully destroyed the body grows new ones at its periphery.
It might be time for the 1064 ndYag laser. I feel that injections are the gold standard and that places that only offer laser do so because the physician is not trained to do sclero with injections. Laser is easier, sounds more high tech, and the doctor can charge more. But injections are the gold standards.
The laser is better at "cleaning up" those small, pesky lingering veins and I would recommend it at this point.