I doubt you'd devalued a your car at all considering it's age & mileage.
I'm only having my car serviced at Skoda due to it's extended warranty with them, otherwise I wouldn't let them touch it. I don't use a main dealer for better service, infract I've known them cut corners on many occasions, not just with Skoda, either. I also replace my own brakes, as they're not covered under warranty, plus I'll save a lot of cash within the process of doing so.
So if you have the ability to service it yourself, why not, something rather rewarding with maintaining your own car to a decent level, do it's yourself then you know it's done right & you've saved yourself cash.