To bad dude, i also had a gd-rom problem but never to the point of not reading cd-r games, only original disks were affected.
I even remember when i used to play PSO quests using the original disk, i remember doing a quest called soul of steel and elenor took 30 minutes to load, so even if the quest is a 3 layer game i played alone since the npcs weren't loading.
After a terrible acident with my dreamcast i bought a new one and not only i swaped the damaged hardware, i also took the oportunity to swap the GD-ROM unit, i never tested it with a original game yet, but atleast i know it's in better shape.
In the end i swaped everything in the console lol.
But good luck with the new upcomming one, maybe that console will help you get back in the game.