I've been playing for about 6 months now and have already started moving on towards harder songs like YYZ and John The Fisherman and such. The issue is, I've really noticed how kinda crappy my current bass is.

I don't know the model exactly but it's an Ibanez that I received as a gift. Anyway, I was thinking of moving onto a Fender bass which seems to be the best thing I can get/afford.

The basses I've rounded it down to are

1. Fender Jaguar
2. Standard P
3. Standard J
4. American P
5. American J

I really want the Jaguar but one thing that kinda confused me about the whole thing is people in forums stating that Guitars that are assembled in places like Mexico and Japan and such are of lesser quality then say a Guitar made in America. Now I would get an American Fender but they're considerably more expensive then the Made In Mexico models (500$ price difference.).

Would a MIM Bass be ok? The Fender Jag seems like a real good choice for me but even that bass isn't manufactured in America, It's manufactured in Japan. So if anyone can please maybe explain to me what the difference would be in sound due to it's manufacturing location it'd be greatly appreciated.
Over-blown long explination in small to save space
Basically, with locations for any instrument, some places use cheaper woods and other materials, have less stringent quality testing, etc.

The reason most people prefer American-made instruments, is because quality testing these is usually tougher (so worse instruments simply don't make it through), and few American-made instruments skimp on materials.
Mexican-made instruments tend to be made of cheaper stuff, but more importantly than that, their quality testing is usually a lot more vague, and the sheer craftsmanship is just never quite as good. Of course, every once in a while a really well built, nice instrument will be made there, but it's nowhere nears as consistent as other countries.
Korea is pretty much in the same boat as Mexico for this, just different manufacturers have factories in different places. Fender tend to get more stock from Mexico, Gibson more from Korea (especially via their Epiphone brand), etc etc.

As far as Japan goes, they're a bit hit-and-miss. I'd put them about in between America and Mexico; it depends heavily on the type of instrument in question though.
One thing to note about Japan though (and to a lesser extent, Korea), is that a lot of instruments made there are heavily machine-made and assembled, while American instruments (especially higher-end ones) tend to be more hand-made. Whether this is a good or bad thing is up to you: hand-made guitars are going to be more thoroughly checked over and had more time and care taken over them, but on the flip side, people do make mistakes from time to time...

For Bass guitars, personally I've found any Japanese-made bass is easily as good as any American-made one I've tried. I honestly have never been able to tell the difference there. When I first started I instantly went just for American-made basses (various different makes and models), since I just figured they would be superior and it's what everyone else at the time said to get, then a while ago I found a Japanese-made Fender Aerodyne J-Bass, and it's the best bass I've had played. Since then I've played a couple more Japanese-made basses, and they've all been gorgeous too (though not quite as nice as my Aerodyne, heh )

On those grounds - I've not played a Jag, but I'd say try it out at least, definitely. If my experience is anything to go by, Japanese made basses are more than fine, and looking at it's techie specs, the Jag sounds like it'd be pretty nice.
have you actually tried the jaguar out though? I mean I thought it looked so cool and thought I would buy that as a new bass, but trying to actually play the thing I hated it. I don't know how something with active pickups can have such a lack of versatility, and it is rather noisy and somewhat uncomfortable. I have heard a lot of other bassists agree, make sure you try it out thorougly before you buy one.

I have to agree that any japanese basses I have tried out (other than the Jaguar) feel and sound just as nice as mass produced american ones. Plus with the fenders a lot of the japanese ones are artist models, so if you have a real specific sound you want to emulate, those are one of the best places to look.