Modifying a Glowforge doesn't make much sense to me when you can buy a more technically capable laser cutter/engraver at about the same price point, especially if you are planning to put money into upgrading the GF. The GF seems to be especially well suited for the crafter that is a little afraid of technology and that needs it for occasional duty.
A 60 watt laser seems like a good power rating if you want to both cut and engrave. If you just want to cut, then I'd go for more power.