Experimental pilot reports flying in very marginal conditions; first climbing then descending through cloud layers before requesting Special VFR at destination.

Narrative

[I] was cruising at 7;500 FT; enjoying nice tailwind; clouds below about 3;000 FT; but clear VFR above. I had anticipated staying on top until I got near destination then finding a hole to get down; but a call to Flight Watch told me that wasn't going to happen. It started closing up under me so I found a hole in the deck and wound up landing at an airport 1/3rd of the way. Waited on the ground for a couple of hours watching clouds and visibilities on the internet; hoping it would improve. Given the very large slow moving front over my route and destination I knew if I didn't get home today I would have to wait several days before the weather would be good enough to get home. The visibility seemed good enough (4-5 miles) to scud run so I decided to make a run for it. [I] got about as far as 2/3rds of the way and it got much worse; perhaps 300 FT and 2 miles. Not having any options at this point; I elected to climb and got above the clouds; about 3;500 FT. I had plenty of fuel but was getting short on daylight. My GPS shows some terrain features; so I decided to keep heading directly towards my destination until I reached the Mississippi river; which would keep me away from any tall towers in the vicinity. At that point; I descended back down through the deck until I could see the water. I followed the river north for a short while; until I recognized a highway that ultimately leads to my destination. I called the Tower and requested s special VFR; which they granted. At that time; I think it was 500 FT and 3 miles with mist and I landed without incident; 20 minutes before official sunset. [It was] definitely a case of get-there-itis and poor judgment. All day I have been thinking how close I really was to not making it.