I'm not sure if this would be "feature bloat" but something that I use another addon for (BigSpender: http://wow.curse.com/downloads/wow-addons/details/bigspender.aspx) is the ability to set a max purchase amount and have the game warn you if you're spending over that amount with a confirmation box.
Replicating the functionality of another addon that does one specific thing would be bloat, yes. Just use that addon if you want something to block you from large purchases.
I'm not sure if this would be "feature bloat" but something that I use another addon for (BigSpender: http://wow.curse.com/downloads/wow-addons/details/bigspender.aspx) is the ability to set a max purchase amount and have the game warn you if you're spending over that amount with a confirmation box.