Well I think I'm just "traditional" in how I manage my content. I don't need an outside source managing it for me. I like to sync my iPhone or iPod through USB as opposed to wi-fi. If I could sync my devices through Bluetooth as they sit next to my computer then that would be great in alleviating cable clutter. They're no point in syncing through wi-fi and using up bandwidth. Any content I want on my phone I can do manually on my Mac then sync through USB to my device. Their may come a time where I no longer have that option but for now I do and it works for me. If I turn on iTunes Match then I can't sync my iPhone in the "traditional" manner. I'd have to turn Match off to do so. Seems like a pain that you can't have both options simultaneously.
I think you're still confused about what happens.
I mostly prefer the traditional approach too, but I have Match. On my iPad I don't store all my music, I use Match when I (occasionally) want to play something on it. However, I also manually manage my music on my iPhone and iPods. It is true that you can't mix manual syncing and Match on each device - but you can choose to manually manage devices, and you can choose whether to add (that is 'turn on') Match on each device that supports it.
Match does not force you to add it to every device that supports it - this is entirely optional. You can choose to add a device, and to turn Match off again later on any device/ additional computer if you want to.
So long as you have one 'master' computer with Match turned on, the other computers/devices can *optionally* use Match for your music, or not, but you still have full control over whether any devices that sync to your computer use Match or not. Turning Match on on one device does not force it to be enabled on other devices.
What I'm saying is, if you wanted to sign up for Match for a year purely to upgrade your 128kbps files to 256kbps files, you can do just that without affecting any devices you sync your music to, at all. Once you'd upgraded your files you could log into your iTunes account and turn off auto-renew for Match, then turn it off in iTunes, and never think about it again.
That said, Match is no absolute guarantee of the files being upgraded (but I'd be surprised if it didn't match almost all of the old files, enabling you to delete then replace them with 256kbps versions once they were matched, especially if they were bought from iTunes in the first place). So this could possibly work out cheaper than re-purchasing them all for you.
Finally, as others have said, if you do decide to sign up to Match I advise you to make a separate back-up of all your music first just in case.
If it sounds fiddly without the guarantee of doing what you'd want it to do that's because it is(!). Good luck whatever way you decide to go.