I agree with most of what's been said here, in fact I made a post not too long ago that explained a bit of cheese that I've found to work and did so in the hope that the information could be used by Stardock to fortify the AI against it and such. I would like to point out however, that it can often be a fine line between clever strategy and cheese. It's a difficult thing to define and most people probably wouldn't agree on everything, especially in those grey areas.
An example of an AI weakness that you can 'exploit' is the whole first-strike issue. The AI doesn't focus enough on sensors and engines and even on a level field, will rarely be able to out manuver a decent human player. This doesn't stop me from designing ships that I know will perform better, or making sure that I initiate every conflict possible. I doubt most players would consider emphasis on first-strike cheesy, though I think there is an argument for it. The obvious advantage of the Eyes of the Universe is a bit more cheesy and I even skipped it a few times, but in the end I found that all it does is save me the micro management of using sensor ships, so I don't restrain myself anymore.
Anyway, I agree that everyone looks for different things in the same games, and they get different things out of it. Some insist on a "level" playing field for all players in the galaxy and are content to defeat the AI at that level whether using cheese or not. Some would rather be challenged and forced to look for and exploit every tactic they can to win (justified by the insane AI bonuses on suicidal etc). Some people prefer to be able to wipe out the galaxy on their own (myself included), while others are content play a small part in an epic conflict (which I would love if the AI were only a bit stronger / agressive / cooperative). I try to avoid what I consider to be extreme cheese, but I am unwilling to give up things that just make sense to do, even if the computer is weak in that area. Should I choose to build my planets in less than optimal ways just because I know the AI does too? Should I wait and let their fleet attack me when I can stop it just to give them first-strike 1/2 the time? I just adjust the difficulty to help compensate and let that be the end of it.
My point is that it is not fair to call any of these play styles any more worthwhile than another. Even people who pull what most would consider extreme cheese to inflate their metaverse scores, they are finding the challenge, not in trying to be a galactic ruler / strategist in a fair or realistic setting, but in analyzing what affects the scoring system and trying to 'milk' it for all they can. Many often assume that the motive is a higly ranked empire / character and that they just want to show off. Although that may be true for some, for others, getting the best possible score can be a challenge in itself. For some who might find the other aspects of the game as no longer interesting, their main competiton may become each other, not the AI.
My attitude / approach to this game seems to be closely aligned with the majority of the posters here so far however, I don't think that I can say that my way of playing is any better than anyone elses. I'm not going to say that people are cheating or deluding themselves by not trying to create the same gaming experience that I am. I can't tell them how to play and I've given up on moralizing these views and play styles because there simply is no ultimate standard, no final word, no god of galciv2 that is going to hand down commandments outlining what is right or wrong (except maybe Frogboy

). It's a game. Have fun with it. Mod it if you want. Play in the metaverse or in your sandbox. Whatever you do though, it might be easier to enjoy it if you spend less time worrying about what others are doing and focus on your own experience.
Wow that ended up more preachy then I expected / wanted. Sorry about that, but it's not quite over.
Concerning the Metaverse:
If someone only plays to pad their scores and show off medals, let them. Why complain about them being able to achieve better scores if you don't care about the scores? Everyone knows, or should know, that the scores are far from being an accurate measure of skill, intelligence, honesty, etc. If you do care about scores, then beat them at their own game, prove your superior ability to manipulate them and play sandbox games or use another character for the fun experience you desire. There is no perfect scoring system, tweak it all you like, but manipulation to an extend will always be possible.
I admit that I like seeing my medals down there below my posts, but you don't have to sacrifice playing games that you enjoy, the way that you want to in order to get them. The main thing I like about the metaverse is that it records your game history so I can always look back on my conquests and laugh about games I had like pushing to tech victory as the Arceans on a tiny map (My first and only tech victory so far.). Fun times.
Now um, what was the O.P. about? Oh right. Geez I talk~er type too much... [/rant]