Okay...sorry it took so long to get back to you. I have a lot of odds and ends I wanted to get sorted out. I took your advice and loaded all the 1820-1840 David Hays and similar spellings into a spreadsheet, then went to the 1830. I agree the 1820 is the David Hays/Mary Horsman family - tracking them forward was easy. Family is well documented and the kids match the census well for each year. In 1830, their David jr. appears to be on the census twice - certainly not mine unless there was a gross error in ages - so mine wasn't in Clinton Co. in 1830. Next I took all David Hays on the 1830 and ruled out based on (1) b. between 1770 and 1790 (2) Martha birth same way, then excluded those without both parents present. If they didn't have females b. between 1810 and 1830 I eliminated them, also slave owners. Finally, I went through and eliminated those I could match to the 1840 census. That left me with 2 in Washington Co., PA and one in Shenandoah, VA (obviously a longshot on that one).
There are a handful of trees that connect David Hays that died 29 May 1869 in Champaign, IL - I was a bit skeptical at some point, but it looks like that may be the most likely one. Thanks! Brad.