What's the advantage of having a spell on your List vs. just using UMD on any old item ...
1) ... don't have to visit a Magic Mart
2) ... X__________________________
2) ... you don't have to spend tons of cash on expendibles
3) ... you don't have to rely on the DM's good graces for buying the expendibles
4) ... you won't run out of expendibles
5) ... if you want to use expendibles then you don't have to deal with the additional potential failure (and losing access to the item for 24 hours if you fail on a nat 1)
6) ... you don't have to spend the extra skill points on UMD/UPD (though it IS a good skill if you're in the position to use it on things you find)
7) ... you can create expendibles if you so choose for less gp than otherwise, which increases your effective wealth
8) ... you can say without reservation that it's your character pulling the weight, not his equipment
9) ... expendibles are far too easy to strip off a character; class features, not so much
10) ... there's more, but I think you get the picture