my view on tempvars is they are another prop/method for simplifying things for those who don't want or have the time to do things properly. Ok they can be referenced in queries - so can a function or reference to a form control. To my mind their main difference is they retain their value in the event of crash - so the developer can simply say 'click the continue button' and carry on and not bother with proficient error handling.
I'm old school and develop solid and reliable applications but I do accept there are a lot of users out there who just want something to work, even if it limps along (much to the bane of IT departments) and for them a tempvar is potentially a big help - much the same as MVF's and attachment fields. After all, Access is a RAD tool and not intended as a tool for developing world class applications. That said, I've developed a large number of apps for clients large and small which are solid and reliable and meet their requirements to the extent they do not need to go looking for a world class solution