EFU:R has been designed to center around player crafting but has failed to address the biggest problem with the crafting system. XP becomes more valuable as a character climbs in levels yet the crafting system doesn't reflect this. Ordinarily I'd suggest that some sort of system be put in place that lowers XP cost the higher the crafter's level, but It seems to me that it'd just be far easier to remove the XP penalty altogether. I believe that the loss of feats and the gold cost alone is enough to regulate the system until there's a better alternative.
I will always '+1' this suggestion anytime I see it, but it sounds like a scripting nightmare. Perhaps the XP can be "given back" after it's taken?
I am 100% in support of either this suggestion, or somehow scripting it so that your class level translates into the potions you brew.
Maybe a temporary loss of experience that slowly returns over time? You're putting your strength/power into those vials and it takes some time for you to recover. Something similar to the new addition to the death system that gives you back experience over time up to a certain %?
I have always found it interesting that the best time to brew is when one is low enough level to make the potions people want, but not so high that regaining the experience put into it is a chore. Sitting at level 9, I do not brew anymore, and I can't fathom anyone who got to 10 would want to do it.
Other flat-ish XP taxes, like curing Withering, made for similarly silly RP. "Oh, it's definitely my character's desire to heal you, but I can't eat the XP hit without de-leveling. Let me brew a potion for you, which takes far less and shifts the burden onto you. Or, you can ask this low-level character who needs only to kill a few creatures in the Worm Pit to make it back. It is apparently less of a burden for them to deal with this terrifying curse than it is for me, a much more powerful servant of the Gods."