I use Gelish on my clients nail enhancements & on my own, it's the only thing that withstands what I do everyday with my nails in the salon.
It does not cost anymore in time than using any other UV dried polish style product over the enhancements & that still needs buffing off as does Gelish - no difference there, however the Gelish bottles are 15ml instead of the smaller 7ml of some other brands, which are more cost effective.
Clients don't want to wait for normal polish/enamel to dry thesedays as there are products out there that eliminate drying time & they are happy to pay a little extra for that - the extra £'s they pay for the Gelish or any other similar product out weighs the issue of it not being dry & able to not worry about it smudging.
If you use Gelish, I would recommend using the Foundation base too over the enhancement, as I would use the base with any other similar product.
You'd be silly to not charge extra for this service - I charge extra for anything I put on thier nails -polish, Gelish, Nail Art - they all end up being buffed off at the next appointment. And we are going to take a file to the nails anyway, it doesn't take me much longer to do that only a minute or so.