I was wondering about peoples opinion on the keyboard. Is it worth picking up? I have the game and have everything but the keyboard.

Depends on a number of things, but mostly how serious you are. In my experince, people find normal keyboard to be too boring or easy on all difficulties, while pro keyboard is is far too difficult (in demand and notation) and people get frustrated with it easily, even on easy.  
 
Not to mention the fact that the only songs that you will be able to use pro keys on (and really, you need to play pro keys to get your money's worth) are the ones on disc. You don't get retroactive pro compatability like with drums and you have to pay extra for any DLC you want to play on pro.  
 
Extrapolate what you will from that. 

I agree with this:

Not to mention the fact that the only songs that you will be able to use pro keys on (and really, you need to play pro keys to get your money's worth) are the ones on disc. You don't get retroactive pro compatability like with drums and you have to pay extra for any DLC you want to play on pro.

But not with this:

while pro keyboard is is far too difficult (in demand and notation) and people get frustrated with it easily, even on easy.

It's perfectly learnable on Easy, even Medium. When you step up to Hard is where it can get tough. As long as you're OK with possibly never being able to play Expert or Hard, then you'll be happy I think.

As an actual keyboard player I just want to use it as a cheap keytar midi controller, but I have no idea how comfortable the keys are compared to regular keyboards :<