Hello, Tatia,
Sorry for these long posts!
You ask some very good questions, although, I think I may have mislead folks a little in my analysis of Culp's TGAH scripts.
I think in general you got it exactly right; the tone of TGAH simply did not wholly qualify for the serious, angst ridden type of episodes that Culp so masterfully writes. While we all love the bantering and fun of the Kelly/Scotty relationship, I Spy definitely employed some serious images, plots and realities about the spy business even outside Culp's scripts. So, taking the script to the intensity of Culp's usual art scored bulls-eyes for the series.
TGAH was certainly meant to be more light-hearted in tone, although a couple of non-Culp scripts, like "My Heroes have always been cowboys" did display some heart-rendering themes, such as having to put one's long-term hero aside when he exhibits flaws too great to ignore. That is a superb, highly rated episode and Culp was perfect in it.
The three Culp scrips for TGAH went from Perfect, Good, Poor in terms of appropriate TGAH fare. The perfect unfilmed Culp Script I mentioned seemed to peg all the aspects of TGAH the show promoted--it had humor in it, an excellent subplot involving Pam and the school kids, an interesting main plot, good use of the suit and great Bill/Ralph interactions. It's really too bad it wasn't produced. The good episode of Culp's, "Lilacs" also had humor in it, and was overall a very respectable show, although the Serious Dialogue Scene with O'Neil was really out of place for TGAH, and was obviously cut straight out of Culp's I Spy memories. Also, the tag scene was very ambiguous and left the audience wondering how the heck things really ended for Maxwell and O'Neil, since she was never seen again. Only "Vanity" really didn't do well, is considered a poor episode, for reasons I mentioned previously.
As for Bill/Kelly similarities, there are, oddly, a few. You pegged a great couple of them. Both had a very vulnerable, sensitive core in their personalities, which Kelly hid with "coolness" usually, and Maxwell hid with tough machismo. But, both cared very much for their partners, and would sacrifice their own lives for them. Both had been unlucky in love--Kelly leaving a serious relationship for spying and Bill having had a wife who apparently died young. (However, Bill was presented as rather asexual, not really interested in women, which Culp hated, while we know that Kelly was one of the most oversexed characters on TV!) Both character back stories had childhoods without solid parental presences. Both were very loyal--to their partners and to America; solid patriots. Both had excellent sense of humor and could be very witty. Both were drop dead handsome, legs that went on forever, and wonderful smiles!
))
Mona