The 37-year-old Langer admitted he has formed a close relationship with pace bowler Caddick and opening batsman Trescothick, the team's best performers in 2007 when the county won the division two title.
Caddick, 39, took 70 wickets at 24.14 while the 32-year-old Trescothick, who had suffered a stress-related illness, racked up 1,315 runs at an average of 62.61.
"Marcus was absolutely outstanding," Langer told the BBC.
"When I arrived it was obviously very public him leaving Australia and the Ashes in what for a lot of us was the biggest series of our career.
"But I love the way he goes about his business internationally and domestically and his contribution in the clubhouse was just fantastic.
"He's a terrific person, a natural leader and his contribution was immense.
"And if you know you've got an Andy Caddick who's going to keep putting the ball in the same areas, take wickets and be as fierce a competitor as he is makes my job as a captain easier.
"It's so good to have his leadership, expertise and pure skill."
Langer said he was stunned that Caddick hadn't added to his 62 Test appearances which have yielded 234 wickets.
"In my view, besides Andrew Flintoff he's still the best bowler in England. His season last year proved that," said the Australian.
"I'm staggered he hasn't played a lot more Test cricket in the last 10 years. In fact, I'm staggered he hasn't played every Test for the last 10 years, that's how highly I rate him."