If you use it to activate redstone, you could make a free diamonds scam like PThagaard said. Yep, that's why I said I would replace the button with a sign.
I was searching at one time to see if there was a way to make a shop sign or chest work like a BUD switch. This subject has been talked about a lot in the past and the impression I get is that there are too many potential problems for it to work well. It would be great if you could automate a casino a sign. What if your dispenser(s) ran out? You or I might keep our dispensers faithfully stocked, but judging from a lot of the shops I've seen, that won't always be the case. We all know redstone can be glitchy. Let's say a redstone access door gets stuck open or closed. How do you determine whether there was a problem and you need to refund some rupees or someone is playing a game with you? There is no guarantee that the whatever it is you are paying for even works. Let's say someone builds a messy redstone contraption that doesn't do what you expected or just plain doesn't work? Builds an automated access door to an empty room or drops you into a pit? A rollercoaster that's missing track? I like the idea myself and there are some things I'd like to try if I could. But I also can see where there's an infinite number of ways to work redstone and by associating it with Rupees there will be problems even if a bunch of rules are piled on. I couldn't find the particular post I was looking for, but JustinGuy mentioned some of the points above in one of them. The way he worded it suggested to me it would never be implemented, even though I don't recall him saying that directly. http://empireminecraft.com/threads/suggestion-redstone-signs.2785/ http://empireminecraft.com/threads/doors.4874/#post-63122 http://empireminecraft.com/threads/being-able-to-hook-redstone-to-signs.4765/#post-58416 http://empireminecraft.com/threads/empty-stock-in-shops.1968/#post-20806
Hmmmm... What if you can ONLY put the sign directly over the note block/jukebox/etc. That way it will directly connect, and not activate a redstone contraption. In addition, in order to alleviate the rupee problem, why don't we take dispensers out of the equation? Jukeboxes, noteblocks, doors, etc, all don't need to be stocked. Or, just take the script that makes it say "Out of stock" when the dispenser is empty, so that no rupees will be spent on an out of stock dispenser? Perhaps that could solve the problems you listed?
Then make the cost for the sign higher 2k even, it would create the money sink they are looking for and the 2k price will deter scammers
From most of the bakery type stores that I see it is about .5r, 1r, or 1.5r per item so on average if you were to SOLELY make a bakery types store you would have to sell quite alot of food to get the 2k.
unless it cost different for different items I.E 100r for a jukebox , 500r for a door , and 2k for dispensers?