Arkyve or some other dude posted soundclips comparing the sound of the MPC 3000 to the sound of the MPC 4000 and nobody could notice a real difference (a lot of people even said the kick sounded deeper on the 4000 IIRC). So I think the difference between the 2k and 1k should be even less noticeable.
The dealbreaker for me (also considered a 2k XL) was that the MPC 2000 XL screens seem to have a lot of problems (stripes showing on the screen and shit) and new screens are expensive. BTW, does it have the 8 outs? Because that costs you an extra 200 bucks or something too.
Another issue is the ZIP drives. I'm assuming you are going to use those for the 2k XL? I've heard those things aren't really reliable (I remember a thread with some dude complaining about how he lost all of his sounds because he had them stored on a ZIP drive.)
Also, you have JJOS, I don't know much about it, I think you could learn to deal with the 2K XL's limitations... but the JJOS has the ADSR function and that is really neat, I wouldn't want to go back once I had that, especially when you sample.
As for the pads... I don't think it's that bad, try the SP 404 SX pads, even smaller and just terrible for playing
