Well the thing is, about what... 2 years ago i flashed my xbox succesfully and have played with it for some time.
Now that i'm starting to get interested again, but before wasting money on blank dvds, is it necessary to re-flash my xbox to a newer verion or something for new games to be played? Or doesn't it matter at all (as long as i keep offline ofc)?

It doesn't matter at all, as long as you're playing offline. If you want to go online and avoid the detection, it's recommended you should flash to iXtreme LT.

Ok cool thanks! For now i'll prolly stick to offline still, play some fun games, and maybe later on some funny offline multiplayer games

Ummm..

The ONLY thing is, you going to be on a VERY old firmware, so you might have to patch the games to play at your wave year.

I can't play Wave 4 games, unless I patch the game to Wave 3, but that takes seconds, but only do that if you are playing offline only.

aah and how would i do that?

yea to play wave 4+ your gonna have to update or patch them

easy to just patch them like speed says.....my 360 is wasting away flashed before LT came out.

There's a download link around the fora somewhere.

All you do is, download a game, and you'll get the ISO and .DVD

Delete the .DVD
Patch the ISO to Wave 3 (takes 5 seconds..)
Run ISO through ABGX to generate the new .DVD
Burn. Play.

However, I have to step in here and offer a word of caution; if you do this, patch a Wave4/5/6 game to Wave3, you WILL be banned. No if's, no and's, no but's... you WILL be flagged and you WILL be banned.

sounds cool thanks!
Even when always playing offline with no internet connection?

Well that's the thing, nobody knows exactly how MS detects - just that they do. The "popular theory" is that disk ID is stored on EEPROM and transmitted to MS when you next go online .. so it COULD very be the case that, even offline, if you play "patched" games they will get reported when you DO go online.