If you go back through the threads on CAL and EVA over the years you will find a few people, like myself, who warn guys away from going to Taiwan as an F.O. Life is just too short to put up with the kind of treatment the F.O.s in Taiwan receive.
As for the contract terms being eroded, that is the case with almost all Asian airlines. In my three years there the package went down by $1000 per month every year. Your contract is the best it will ever be on the day you sign it. If you can live with that and live with a 20 to 30% decrease over the life of the contract then go for it. Don't expect an upgrade and don't say you weren't warned.
If you need the experience to make a another step in your career than it could be worth it, but be careful.
Typhoonpilot