Answering Desirae first.
You would be surprised. I used a LR catalog on a laptop taking thousands of pictures a week for years without it slowing down. My advice would be to keep on trucking. Don't change anything. If the machine starts slowing down then it's likely HD issue. So you can delete old LR backups to help that. If you notice LR itself slowing down then you can experiment with making a new catalog and seeing if that helps. I don't think you will experience this for a long time.
Tio answer your question though, yes. If you make another catalog then all your smart collections won't work across two catalogs.
My approach is one catalog. This may sound like not taking my own advice. But I actually use multiple catalogs for work that does not need to cross pollinate. I used to edit for another photographer, and had a catalog for that, photograph for a newspaper, had a catalog for that, photograph for my own business, catalog for all client work, and a fourth for pictures taken as a hobby or of my family and friends. Those catalogs never needs to interact with each other. And keeping them seperate made it easier to find stuff while performing one of those tasks. That is the ONLY time I recommend having multiple catalogs.
Now file management is a separate issue. I have a workflow that works great for getting the originals off of the computer but still having this cataloged by LR.
For Igor. No, please don't do this. Just use the import feature on LR straight from the camera card to the main LR catalog. Your current workflow won't actually break anything. It's just ridiculously more complicated for no benefit I can see.