I have router ski jigs, router jigs for planing (rails and jigs to ride on those rails), bottom cleaning planing bits for my Radial Arm Saw, etc...
I have those for odd sized pieces that are too large for my thickness planer. Planing with a router is a bit slow and tedious. I use 1-1/2" to 3" surface planing bottom cleaning bits:
http://www.magnate.net/index.cfm?event=showProductGroup&theID=136#
http://www.amazon.com/Magnate-Surfa.../B009X5MZ74/ref=sr_1_1?s=hi&ie=UTF8&qid=1380760871&sr=1-1&keywords=magnate+2709
They still take a while, but when I have something 36" wide and 20 feet long...
Second to the time and effort is that that the finish quality is somewhat rough. It will leave light lines where the cuts transition from one cut to another (pass to pass)... which need to be sanded down. They usually don't need much sanding to make them go away, but they are visually there.
Especially for what you plan to do, a good thickness planer would be a good investment. I don't have a Dewalt. I have a Rigid. Both are good, but other owners of Delta and Steel City have good things to say about theirs also.
Research on those. Check reviews. See if you can test drive one somewhere. Check the initial prices and the long-term prices of expendables. The expendables include the blades (cost of replacement, can they be resharpened).Once you pick one, decide whether you want something new or if you would be happy with something used. If new, look at the warranty. A lifetime guaranty can go a long ways. If used, decide on alternate choices. Then check Craigslist...
You can do a lot in short time with a thickness planer. There are also jigs and mods that can extend the capabilities of or to make things you do with it easier and/or more accurate.
Good luck on your decision. If money is tight and you have a router, go with a router jig until you can afford a thickness planer. That will give you the capability until you can.