People leveled their warriors prot and their mages arcane even before they got awesome. Sure another tree or spec would've been faster or better but if you want to stick to your decision and you don't like shadow then I'd say go for Disc.
Plus you can heal instances even better, sure a shadow can heal a 5-man but still it's more fun that way.
well i been leveling disc from 1-61 lol and for sure im gonna stay disc in northrend, imo its better than shadow :P i never go oom and my heals are leet