I can try to break it down further. Between 1972-1973 Bob was just getting the feel of the show. His interactions with contestants was brief and he would play through the at the time limited library of pricing games. By 1974, the audience had more freedom to shout out prices and the level of excitement was enhanced, which I think improved Barker's hosting, and he was more conversational with the contestants. However, the show also had a glaring problem that there was too much "show" for a half hour, so thankfully the show was expanded to an hour (which translates to maybe 50 minutes of airtime with commercials).
By the time the show went to a full hour, Bob had the show down, and having more time to play with the contestants made him more relaxed. When Dorothy Jo died in 1981, you could notice a slight difference in Bob's demeanor. The episode where he acknowledges Dorothy Jo's death, he's conducting the show as normal, but you can still see a dark cloud over his head. However, he eventually gets past the sad event and things seem normal.
One key ingredient that made the show work so well was Johnny Olson. His immense talents and williness to get into funny costumes and do various dialects, made him a perfect second banana. During the 1984-1985 season, it's noticeable that Johnny's announcing voice is starting to sound tired. It wasn't because of boredom, but because of old age, as he was in his 70s. As we all know Johnny died in 1985.
During the audition process, it was jarring to see TPIR without much interaction between Bob and the announcer, however they found as close to a perfect replacement as they could with Rod Roddy. Rod was funny, and also willing to get into funny costumes, and while it would be unfair to compare his onstage talent to Johnny's, I think Rod still did a splendid job. However, Rod's involvement with the showcases would decrease over time as well as his appearances on camera.
However, in the wake of the Dian Parkinson scandal, Bob's demeanor changed drastically. He became more impatient with the slower contestants, he stopped flirting with the female contestants, and also stopped interacting with the models (which was no surprise knowing what we know now) but he still had his good days.
By the show's 30th year, Bob skipped doing any opening monologue and went straight to "here's the first item up for bids". He also almost stopped talking to Rod Roddy altogether, and Rod's overall presence was limited to the show's closing credits, then he didn't appear on camera at all with the exception of the 32nd season premiere.
When Rich Fields came into the picture, Bob's interaction with him was limited, but it seemed to me that his demeanor was more positive. I would dare say that Bob's hosting was the best it could be during his last year as host. I think since he knew the end was coming, he had more fun, which is far better than pulling a Richard Dawson and having a dark cloud over his head.
