go to a home store and step into a 3 foot shower and see how you feel compared to a 9 foot spacious shower. with benches built in.

I can not agree with more. Most people do not realize the a 4 foot 6 inch vanity is just too small for two sinks for the shower/bath model.
I also agree with the post from Dgustaqf above space needs to used wisely and the added benefit of handicap access would be huge.
In my master bath remodel I removed the bath and went with the low-profile Kohler cast iron shower ban the same dimensions of a tub. What a great spacious shower and no risk of falling/slipping in a tub.