The "High Street" is changing but it always has. Yes, we are losing lots of big names, but look at the new shops replacing them. New Look is a big player now, that hardly existed some years ago, coffee chains, etc, and who'd have thought a few years ago, that shops would open where you can go and have your feet nibbled by fish.
The public are moving away from buying "stuff" from the shops, they can get that online, but people do like to go out, and shops need to be more leisure based, such as pubs or restaurants. I think a lot of the big players will try and keep a site on the high street, but only to act as a "shop front" to their online business, so customers can collect / return orders, or go in to have a look at a product.
It would be a shame if Chesterfield tried to compete with the likes of Meadowhall, it will fail. And the council should NOT spend money on new buildings (which don't stay new very long), while there are old buildings sat empty.
What the council should do is play to Chesterfields strengths, people will visit the town if its a good place to visit. (And that includes appealing to tourists as well as local shoppers, as we are ideally situated with M1 on one side and all that lovely countryside on the other.
So what the town centre needs is lots of parking, (free or cheap), lots of clean toilets, etc, sheltered and pedestrian areas, to feel safe, ( security cameras and police on beat), places to sit, places that are interesting or attractive to look at, etc. So the canal side development should go ahead, lets get a few small bars and bistros, etc, there, some boats on the canal, a few small green areas. If the donut is going to be developed lets not go for the obvious choice of retail units, how about an indoor skiing thing like Milton Keynes, or some sort of internet cafe/library/technology centre, a small music venue to compete/compliment Winding Wheel, a dance center (strictly is very popular at the moment), a planetarium, ( stargazing is suddenly very popular). The point being that shops are not the future, leisure activities are what will bring people to the town, but it needs to be done in a way that doesn't spoil what we have, as Pete said, we don't want to be "another typical sh*thole town".
PS, just heard that Screwfix are opening on Derby Road.