I would like to suggest an alternate path.
Try adding an adjustable level cap that allows a lv.28 player to be capped at say lv.18 before they enter a quest.
This solves any problems finding members as long as they don't mind none epic content.
Higher level players may choose to join any lower level quest without penalty to experience.
This is similar to what was done with my old MMO FFXI it worked out great! (Once all the bugs were worked out)'
Thank you for your efforts and accomplishments you have made with DDO cant wait to see where it goes from here.