I was reading through your post again and just caught your edit. Also kinda glazed over this first point about the unlocks.
Quote Originally Posted by Amineri View Post
Retainers
I'm a bit torn about the mechanism to unlock these retainer abilities. In part this is motivated by the lack of good in-game gil sinks, and in part by an aversion to eventually seeing every player have all abilities on all retainers. Just as the 'ability slot' system limits (to a certain degree) the number of abilities a character can have equipped at one time, it seems to me that there should be some negatives to having all of these abilities.

To that end, I would suggest that the quests that origamikitsune suggested be there to unlock the retainer abilities. The quests unlock the ability to purchase retainer licenses that grant the specific ability for a specific time. This makes the retainer abilities an a la carte feature, rather than a package deal. This clearly wouldn't work for some of the abilities, such as increased storage or bazaar space, so these would have to remain permanent upgrades.
You have a good point- the requirements for upgrading (spend gil, do quests) really cannot be viewed as negatives. Using the "a la carte" method reminds me of the other discussion where it amounts to an annoyance such as paying bills every month. I guess it boils down to the truly important upgrades remaining permanent vs. fluff being renewable. I could rationalize buying temporary customization options, and extra retainer bazaar slots.
Quote Originally Posted by Amineri View Post
Regarding increased storage, I concede that increased storage is necessary, and currently increasing retainer storage space seems like the only choice.
While i was rummaging through the "Ask the Dev's" ealier I found a couple relevant statements:
9/29/10
Also, we are now taking steps to increase the number of retainers that a character is able to simultaneously employ.
1/24/11
Q.When will players be able to hire more than two retainers?

A.Currently, we intend to allow the hiring of additional retainers once all planned system changes have been executed. The ultimate date of implementation, however, may change depending on player response to the changes.
Adding one or more hireable retainers would absolutely alleviate storage concerns and the need for the level 1 upgrade I suggested. Furthermore, given enough storage I wouldn't be tempted to purchase an additional charater for storage- eliminating the need for level 5 upgrade. Your "a la carte" system of buying desired customizations and access to the World Market would make an ideal solution with those facts in mind.

Throwing more retainers into the current market system results in Ul'dah bursting at the seems.