Should I upgrade?

It would be considered a downgrade. The ASUS X200CA has the Intel Celeron 1007U CPU which is based on the Ivy Bridge generation CPU. They Asus Transformer has the Intel "Bay Trail" generation Atom Processor Z3740.

Despite the fact that the Z3740 is a quad core CPU, there is a decent amount of performance difference between the Celeron and the Atom CPUs. The Celeron would be considered a powerful dual core CPU. I would guess-itmate that each Ivy Bridge core is over than 2x as powerful as a Bay Trail core.

Additionally, you would be limited to 2GB of RAM which is rather lacking in my opinion. Windows 8.1 can run with only 2GB of RAM, but if you are the type who likes having a lot of programs open, or many tabs open to browse the internet, then the limited RAM might be a problem.

The only "upgrade" aspect of the Asus Transformer is that you can use it as a tablet by detaching the keyboard.

I was going to suggest that you wait a little bit for a netbook using Intel's Braswell generation Atom CPU, the successor to Bay Trail, but it was announced 3 days ago that Intel decided to push the release date to June 2015 because sample testing reveal that many Braswell CPUs were running at clock speeds too low to be worthy of being called Bay Trail's successor.

As it stands right now, if you are looking for a low price alternative to the Asus X200CA, then I recommend you wait and probably save up some money. Intel will be releasing their next generation desktop / laptop core i3/i5/i7 CPUs (Penitums and Celerons too, but later) called Broadwell this December. You may need to wait 3 months for the lower end Celeron / Pentium CPUs to be used in laptops though.