Fates outside of Coerthas Central Highlands and possibly crystal farming aren't going to be very active on any server, and post-50 you're better off doing beast tribe dailies and Centurio hunts while in queue anyway. Not that there aren't good reasons to want a larger server - PF pugs for harder content are more feasible, and the static raiding system is a lot more functional when quality subs aren't non-existent (though perhaps raid finder helps here). But your $18 isn't going to a ton for your solo leveling process.