I'm glad this thread is still alive. I'd like to see this idea develop into a formal 'suggestion' adhering to the requirements to get something in front of the devs via the Ideas/Suggestions forum here. I'd like to see this building added, even though I consider myself a 'combat only' player. I agree it will not help caterers 'catch up' even a little bit with fighters, but that doesn't mean the building has no value.
To help explain why it won't be of 'limited' use to fighters, at least in the tourneys:
A side effect of being a fighting city is having a huge inventory of goods. I've teleported out all my T1, 2, and 3 factories from both cities and only place them for event quests and FA's. I still have millions of each good. They come from having factories out during events/FA (if they're taking up space they might as well produce!) and from buildings that I've placed for other reasons, mainly to provide a link bonus in sets to buildings that produce something I want (mana, CC's, etc). I prefer combat; I prefer manual combat. It's a part of the game I enjoy. I also like consistency, so I tend to try to always do the same amount in tourneys every week. I'm not a competitive tourney player. I like to keep my tourney average in the 3-4K range. Right now, I've settled into 5 rounds of 20 provinces every week though I will do some of the 6th round some weeks. I like to place the expiring military bldgs late in the week so I can get the use of them for 2 tourneys and the Spire (I have the TimeWarp and a lvl 10 Polar bear to speed up the cooldown between rounds). Real life makes my in-game time less predictable every Thurs-Sun, so I like to get as many rounds out of the way by Wed evening as I can. During this event, I got out of sync with placing my military bldgs due to placing them when I wanted to do the tourney/spire for some of the event quests. So, this week, I catered the first 3 rounds of 20 provinces in both cities to get some done and placed my bldgs Friday evening for rounds 4, 5 and a few round 6. I've even recently started catering provinces 17-20 for all rounds just to have somewhere to use my excess goods. I saw barely any impact on my goods balances. If it impacts my coins/supplies, I have plenty of instants. It did impact my mana since I'm trying to upgrade my TimeWarp in both cities and it's taking 500K mana each level for those upgrades now. But, I have a Dragon Abbey and thousands of EE spells I rarely use, so I just made my cities sparkle (for a week or 2!)
For me, it wouldn't impact my Spire much if at all. I go to the top every week and have for over a year in both cities. I think I used diplomacy once in one city when it first came out and since then I may have resorted to diplomacy one other time when a fight was giving me problems. I just don't like it. And it takes sentient goods. There's a huge demand on those goods for other parts of the game (research, upgrades, guest race bldgs, etc) and they decay daily.
I would use this bldg. Just because I have an abundance of goods doesn't mean I'll just throw them away if I don't have to, lol! Since it would go into the 'bldgs' slot in crafting, it's not like I'd have to choose between crafting it or crafting a military bldg. So, I'd craft it every time it came up. Once I got ~5-6 in inventory, I'd start placing it every week. With the current structure of the tourneys, I can see competitive tourney players doing the same and making use of goods to supplement their fighting.
But just because it won't solely help cater-only cities doesn't mean they shouldn't have something to reduce their costs. Cater-only is a valid choice. It's a much harder way to play and should be respected for that level of difficulty alone. I'm not opposed to something that will help them. It's just not going to make them competitive for top rank in tourneys against players willing to make use of all of the tools provided.