AJ,
Me too. I build custom shopping carts using very much the same methodology that you described. However, I normally charge clients a fair degree for a custom build.
If they come to me with a limited budget - then I cannot afford to spend that amount of time on doing it my way.
Having searched the internet several times over for a cheap and effective shopping cart. I have built using actinic developer, get trolleyed etc... and searched high and low for something that allows me to use php if I want to add extra features in -- x-cart wins hands down.
I am not biased in any way, but x-cart gives me the ability to customise just enough to make my clients happy or the reasonably easy middle ground of adding special bits in just for them.
Now I love hand coding in php and would far prefer that to buying an off the shelf cart but business is business.
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ex x-cart guru 
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