Teesside Airport's proper name is Durham Tees Valley Airport, and yes, may serve quite a small market, which is the whole of Teesside, and much of County Durham,
Yes, the rail service isn't decent to the station, however there isn't the need, considering you can easily park your car in the airport itself, as its just had a huge facelift, and loads of extra car parking spaces, aswell as a direct bus link, from Darlington station, via Town Hall and onwards to Airport.
Airport station is a fair treck from the actual airport itself, and is situated in a in-practical location, to serve the actual airport itself, and would be much easier to get off at Dinsdale and walk!
Realy, if the station wants to prosper, then it needs re-locating further towards Dinsdale, and some form of bus link from the station itself, to the Airport. This would most likley incourage use of the station itself
And issue of parking at stations, most stations in Teessdale offer Free parking! Theres only realy TPE managed stations (Thornaby & Mboro) where you have to pay & display!
(As you can guess, I live fairly close to the Airport)