Just an advance FYI, I am primarily a console gamer, I don't PC game much at all. This post discusses my console and handheld game purchasing.
I know people have different ways that they collect video games. Some collect by genre, system, era, etc., but some of us have a bit of everything. Like many members here game condition and completeness are important factors. I try to buy new over used when I can. But I have other rules that I follow when making buying decisions. I haven't always had these rules, and I add more when I need to address current trends. These rules help keep my purchasing manageable for my budget and living space. These are very loose rules, I can sometimes justify breaking them.
1. Only buy games that I like or think that I will like.
This seems like a no brainer, but I don't really buy games for their collectability, or because of the popularity of the franchise. The vast majority of the games in my collection were chosen by me because I found things that I liked about them, regardless of popular opinion or review scores. I have moved away from buying a game that I don't like much because it is 'significant' in video game culture.
2. It is okay to abandon a franchise or character.
This is a pretty bitter pill to swallow. Part of being a completionist is trying to have every sequel, spin-off, or derivative of a game that I love. Characters such as Sonic the Hedgehog, Crash Bandicoot, and Spyro the Dragon have forced me to make an evaluation of game quality before making a purchase. Which leads me to #3.
3. It is okay to buy a good sequel without having every game in between.
4. I try not to repurchase games I already own (ports and compilations).
Games are frequently ported to other consoles and reissued as compilations and I think that's a very good thing. But I usually own the original releases. Unless they have added something significant to the re-release, I try to avoid spending money on the same game again. I am missing out on things like HD textures and trophy support, but I also like the purity of playing a game on it's original system.
5. As a multi-console owner, I try to buy the 'superior' version of the multi-console game I am buying.
Sometimes it's obvious which version is better due to exclusive features or imperfect porting (see Bayonetta or The Orange Box), other times it's not so clear and each version has separate strengths and weaknesses. I try to do enough research and pick the right one for me. This has influenced me on #6.
6. I can buy a 'Playstation' game on any system I please.
What I mean is that Crash Bandicoot, Resident Evil, Silent Hill, etc, are historically tied to the Playstation. It feels 'right' to play these games' sequels with a Playstation controller. But if it makes sense for me to, I'll buy a sequel for a Nintendo system, or a Microsoft system, or whatever (I think this rule sounds lame and obvious, but I have two friends who disagree with me and remain console specific for certain franchises). On what system will I buy the new Tomb Raider? I don't know yet!
7. All other things being equal, I purchase physical media over digital (download) media.
I am not an staunch opponent to digital purchases and I have made many. But it usually makes sense for me to buy the physical media.
As I think of more rules, I might edit this post.
What rules do you follow for your collections? Are you in charge of your collection or vice versa? Does it require this much thought and planning, or are you more relaxed about it?