There is nothing greater then the feeling of doing somthing yourself.
I have bought afew pre mod cases, and have had many sponsors send me some sweet premods as well but I still use my old modded enermax ( Once a premod re-mod )
Sure with the money you would end up putting into a case buy adding windows, paint, extra exhaust hole and fans you could most likely get a really nice case. But when you have the bug... You have to mod.
Look at all the Lian Li cases you see out there, sweet cases and no reason to mod them, even the people that own them say they never will. But you will, one day you will get the itch to grab your dremel and start hacking up your case. And if everything goes well, you will enjoy that case even more after then before.
Here are some things I did to my case that may give you some ideas.
Harddrive window mod on my enermax.
High Gloss black.
Here is my quake super tower of power. Its not finished yet because I don't have the time.
The idea was cool in my head but I had no idea how much work was involved.
Like I said, the quake case is not done yet, and really does look better in person, the paint is much nicer then it looks.