I have no idea why would you want two machines to do two things when you can use only one for everything and not lose anything, but whatever floats your boat in that matter, it's your choice!
About NTSC VS PAL, it is in your best interests to go for the NTSC version first in most situations.
Why? Because the vast, vast majority of PAL games of old played in 50Hz, meaning, they would play slower (around 16%) and could look stretched or squashed, depending on the system. So if a game ran at 30 FPS originally, it would be at 24 FPS in PAL, and if it was at 60 FPS originally, it would be lowered to 50 FPS.
It was only after the Sixth generation where in PAL territories we could start seeing PAL games with 60Hz option starting with the Dreamcast, that would make those games run at the intended speed and resolution they were designed to be.
This means that, yes, GameCube games could be PAL with 60Hz support option. The Problem is, not every game does, and sometimes they're very inconsistent with which games had it and which not, even from the same developers or even series. PS2 had it much worse than GC, though.
The funny thing is that if a PAL game has a 60Hz option, and it works well, then it's kinda superior to the NTSC because PAL also includes more languages and often it's a more updated version of the game (for example, it may have some bugs fixed that could happen on the NTSC version).
And if you play these games with Nintendont, you can force Progressive Scan on PAL games working at 60Hz so you can get the complete package. Progressive Scan has already been mentioned, but in practical effects it makes the picture better all around (at least on the screens I've tried it on, it always gave me a better picture, more clear, which is good for text). You'll need your Wiis with component cables and 480P option enabled.
So the core of this matter is simple.
IGNORE EVERY PAL VERSION OF A GAME AND GO WITH THE NTSC UNLESS:
They have a 60Hz support option.
The can be forced or patched to play in 60Hz (like several games I made patches for).
They're the only version in a language you can understand (Like Doshin The Giant).
The PAL version has something different and of value (Like Luigi's Mansion).
You don't care you're playing an worse performing version.
I personally see no value in playing a game on my language (Spanish) If I'm going to have a miserable time playing at a lower speed, so I'd take a game in English and correct speed any day of the year.
Check if the game you want has 60Hz Support on the PAL release. If it has, then you can try that one for whatever reason you have. If it does not have it, you go for the NTSC version, which will play at its intended speed and resolution.
You can look for lists of games that have 60Hz Support, and you can go visit Romhacking.Net to look for the patches I made to transform PAL 50Hz games into 60Hz if you want.
About games with noticeable differences between regions, Luigi's Mansion is one of the biggest ones, but also know that Dragon Ball Z Budokai 2 PAL had both English and Japanese voice acting plus some costumes exclusive to it. The Viewtiful Joe games have subtitles in the PAL releases while the NTSC ones do not. Donkey Konga 1 and 2 also have different soundtracks between regions (and also including Japan, not just America and Europe).
The Legend of Zelda: Collector's Edition also has some good difference between regions; Majora's Mask has all the languages found in the original PAL Release, but every single game in that collection works in 60Hz instead of 50Hz. In fact, to this day if I remember right, the only legal way to play the original Ocarina of Time, Master Quest and Majora's Mask at their intended speed in PAL territories is through that (and the Wind Waker's Bonus) disc. Quite sad to think about.
Edit: I also remember that there a handful games in which the NTSC version is just the best one. Two of those games are Billy Hatcher and Sonic Heroes, they have native Progressive Scan support, all the languages of the PAL, and their frame rate is better than the PAL versions, at least, on my own experience.
