Ok, I have lots of ideas. If the picture is what you currently have it looks like a simple figure-8 inside of an oval. Are the two totally separate? Is there only the one train or are multiple run at the same time? Is this a simple AC power supply or do you have Lionel's or MTS's control system?
What exactly do you think it is lacking?
Idea:
1. Put two turnouts on the figure-8 so the train can reverse itself.
2. Add a turnout on the outside loop for a stub end siding that fits into the narrow part of the figure-8.
3. Add two turnouts connecting the two loops together so the train can move from one to the other.
4. Add four turnouts and a crossing at one end connecting the two loops together so that a train can go from either loop to the other in either direction.
5. Totally remove the inside figure-8 and replace with lots of industries to switch cars in and out of.
6. Totally remove the inside figure-8 and add two passing sidings to make a single track mainline where two trains can meet and pass each other.
Some of these ideas are obviously mutually exclusive.
I don't know how many of these would fit on a 4 x 8 but there are lots of good ideas. Note especially O-2, O-3, O-7.
http://www.atlaso.com/O%203Rail%20NS%20web/index.htm