Thought I'd add my (late) input to this thread, in case it's still relevant to the OP, or anyone else.
We've just moved to Sandgate from Beaconsfield in Buckinghamshire, we've been here for two months. My husband commutes to London where he works in technology for one of the banks. I'm a freelancer editor and work from home.
The attraction for us was the ability to live close to the sea, still be commutable to the City, and to reduce our housing costs. We bought a lovely semi-detached in Sandgate for a fraction of what it would have cost us in the City or in Bucks. Yes, we could have afforded two or perhaps three times more, but it's a lovely feeling paying a small fraction of your income into a mortgage.
As for the town itself I had some of the worries expressed above too. For the most part they've proven unfounded. Yes there are some grim parts of town, but you can say that about most places of any size. Sandgate is lovely, if still a little run-down in places. On a sunny day, when the wind is down the beach is stunning. The sunsets are really lovely too. The neighbours and locals have all been so much friendlier than in Beaconsfield, and more authentic in their interest in you, if you know what I mean. I personally found that area of Bucks to be extremely snobby and "keeping up with the Jones" for my taste, and it's a relief to be in a more relaxed environment.
The Folkestone town centre itself is rather shabby. It's proven tricky to find decent Thai food and the like, but you can't have everything. Sandgate has some nice cafes (Loaf is fantastic) and Hythe is a bit posher and therefore has a sprinkling of quite nice restaurants. If you need more of a big town feel there are decent facilities in Ashford which is only a 15-20 minute drive away.
Living in East Folkestone is probably to be avoided, there are some seriously grim bits of housing there. Sandgate, some of Cheriton, and Hythe are all nice. We are within riding distance of the station here in Sandgate. Folkestone West is adding 200 parking spaces so people must be waking up to the place being a reasonable commuting option. It amazes me that it's taking this long, but then I think it's easy to be put off by the less salubrious parts of town. The regeneration will be a slow process, but you can see that the foundations are there.
My husband is finding the commute manageable. He works in Mayfair and finds it takes 75 minutes or so all up, door to door. It's not great, but manageable, apparently, particularly if you can work on the train.
In summary it's not perfect, but if you choose the right part of town it's remarkably good value for money.