I don't think we should feel that sorry for the players being stuck in scenarios like this - the reason they want to sign long fixed term contracts in the first place is the security of the income.
I doubt Soldado will want to go back to Spain for a few more years when the salary he'll command will be far less than staying at Spurs until the end of his deal.
Depends on the player there are some in it for the money but I do think alot genuinely want to play football and may see moving to England as a great opportunity beyond simply getting cash. Football is a short career and and if I was good enough to play at a high level I would want to make the most of it personally. Hard to generalise as I am sure there are players happy to warm the bench.