Help! TerraTrike 24-inch wheel upgrade package?

I've been riding a TerraTrike Rambler since last August (2013). Am recovering from a stroke (Sept. 2012) otherwise I'd likely be out on my good ole (1987)Specialized Rockhopper enjoying pretty, easy dirt trails. Got more into hiking and backpacking as time went on, before the stroke, which followed a major fall and various operations.

My Rambler has 20-inch wheels, which are standard for it. It also comes standard with pretty much treadless tires for street or hard-surface trail riding. Also of note, the very long chain is maybe a half inch off the ground by the back wheel when in low gear. The tires and low chain both bother me, as I'm more of a dirt, natural surface trail or even gravel girl at heart. Heck, these tires spin on grass trying to ride out of my grassy yard in low... and the chain is pretty much sitting in the grass when the trike is parked. (note the low chain in the photo)
I am debating a $400 (before labor) package upgrade now offered by TerraTrike to 24-inch wheels with more tread on the tires, yet a middle ridge so there's hopefully less rolling resistance on hard surfaces.
I'm trying to figure if just putting on 20-inch tires with more tread would be good enough and of course save money... although the low chain really bothers me. I also don't know about added wind resistance -- if any -- of 4 more inches in height.
I don't know if my trike would "officially" be allowed on our local state forest road/trails, which are nice and wide. If I were restricted to places with single track, they're farther away... and I fear the trike might well be too wide. (As a side note, I do have a basket on it and would love to combine that with a pannier I bought to do some simple tent camping -- with my typical gear needs whittled way down. )
Anyone have advice? More factors to consider? I've never been much of a road or bike trail rider, although I am now by forces beyond my control. I do like it and the many miles of paved bike trails I easily reach from my home (half a block away to a trail by a river ) are gorgeous... but natural surfaces and terrain call me.
I need to get this decision made...HELP! And thanks!!

 

I need more posts to be able to link to the 24-inch wheel package info. Working on it.

 

OK, this is No.4... my next post is golden.

 

Finally, a link to product I mentioned

Here's a link to info on the TerraTrike 24-inch wheel package.
http://shop.terratrike.com/product-p/all-road-wheel-package.htm