Bristol Temple Meads, possibly over-engineered?! No chance. This station is always busy, especially at peak times. Personally I'd want to engineer it more, in particular make platform 13 a through platform as a back-up for platform 15's through line.
Dorchester South is used as a passing loop most of the day, so it's two platforms are used regularly, thus this station cannot be even considered over-engineered. Same thing applies to Weymouth, and for that matter many of the stations listed as debatable. Harrow and Wealdstone, OK so the fast line platforms don't see much use. That applies to the majority of stations between London Euston and Northampton, as well as from London Paddington to Didcot Parkway. If the fast line platforms saw regular use it would stuff up the express services. Take away the fast line platforms, and you lose the flexibility.
Hooton I saw mentioned and I agree it is a bit over-engineered these days, as those two bay platforms don't see use these days.
There aren't that many stations which can truely be described as over-engineered, just poorly so these days. Stratford International is definitely one that was over-engineered, but I do recall the plan was to stop Eurostar services there originally, then the plan changed after construction started. I could be wrong on the latter.