hard drive upgrade

Macbook duel core- around 2008. running 10.6.8.
Running out of space on the 160 GB drive, So got a 320 to install.
The mechanical part is inconsequential to me; Following the data transfer instructions provided with the new drive seem fairly straightforward.
The problem is that the current drive is full of junk, garbage, detritus.... And a simple "clone" transfer may not be what I want. ??
Should I just spend the time cleaning this out- before or after transfer.....?
I have an external firewire 1TB backup drive via time machine- which I have only used in the one "no problems" direction. An enclosure came with the new drive.
The macbook has no operational issues now- But I have had to reinstall osx twice now (thus, the backup) -> Re-establishing all the configrations and other things, while being good practice, wasn't really enjoyable- and better not to repeat it!-
I want to end up with the 10.6.8 osx version- keychains, contacts, mail, etc intact-> and transfer other selected items only- whatever is contained in the old drive can stay there stored on a shelf.
Is this process (partial transfer) worth it? If so, which direction to go.....?

Personally, I think it's easier and more effective to start over with a fresh install and copy what you need, then to try and thoroughly clean up an old install. I had been using the same installation for 2-3 years and wanted to start over fresh with Lion. I installed a fresh version of Lion and manually copied over what I actually needed. My used space went from 220GB on Snow Leopard to 100GB on the new Lion install.

Go through your current Applications and make a list of everything that's installed that you really need. Swap the drives. Install a fresh copy of 10.6.8. Put the old internal in the external enclosure and slowly copy over what you need. If you miss anything, you can always go back to the external to get it later.

If you take the time to do it right, you'll be glad you did.