MacBook – upgrade MacBook Pro 13″ with HDD

It depends on your project size, but an SSD is unlikely to make a huge difference in compilation speeds - it's almost entirely a CPU-bound task. However an SSD can still make a big difference in your productivity with Xcode, and OS X in general. It particularly helps when you're indexing files in a project, or searching the documentation.

You'll also notice a big improvement whenever you're swapping to disk (e.g. if you're doing another task while a big compile is happening).

Unless money is very tight, I strongly recommend getting an SSD. You can save a lot of money buying a 3rd party SSD and installing it yourself (which is pretty easy in a MacBook Pro) - prices have been dropping sharply lately, I'd estimate about 50% from where they were at the start of the year.

I upgraded a similar era Macbook a while ago. In all likelihood you are unlikely to be able to buy an SSD that will not max out the BUS speed available to it on a machine that old.

That particular Macbook has a SATA I (1.5Gbps) interface for it's existing hard drive. SATA III (6Gbps) SSD drives have been the standard for many years now, although you may be able to get a bargain bucket SATA II device (3Gbps). Basically, I would get the cheapest SSD you can for the capacity you require that is at least SATA II (you don't need it for the speed, but a SATA I one will be based on older technology that may have a shorter lifespan than a newer drive). It is almost certain to be faster than your machine can handle, so there is no point getting a particularly recent or fast one.