A slower experience gain overall (more balanced) impairs the players (not me) that play multiple characters. It means they have to dedicate more time to advancing their characters than they would have had to previously. For someone playing one character, as you've stated, there will be no effect.
I think this will definitely disappoint some players who already felt they were leveling multiple characters slowly.
Assuming it affects them. The change is relatively new, so if people have been feeling it for a while, it would be have something different. Also, the XP gain for roleplaying has in fact at the same time been slightly increased.
Evaluating, I've only seen
very few who has an XP buffer that suggest that they are gaining less XP than will in the long run be their limit,
so I think we should be cautious about speculating too much. Those I've seen at the "strong urge to learn more" level have seemed to be characters that have either not been played in a while, or largely dedicated on social roleplay (which for the record, is by no means a bad thing, but from an IC logical perspective, they wouldn't progress as quickly.) All others will be gaining at the same rate as before - and high levels have always been levelling very slowly.
Now the most important change has been to reward much less for things below your level - in the hope that higher levels will seek out high level dungeons for challenge, rather than grinding the somewhat lower level zones. Without judging too much, perhaps that's the tendency that should change. That's the parole of the system, somewhat: Seek true danger once rather than repeating the trivial ten times.
All that said, please, help in evaluation is always appreciated.
