Originally Posted by rubiksoval

If you want to gain speed, you can do that regardless of whether or not you improve fitness.

If you want to increase fitness, that may or may not be reflected in your speed.

Since you mentioned speed in the OP: 2-3 mph can potentially be gained by A) a more aggressive fit (may or may not improve total overall speed as you have to actually stay in the faster position for significant amounts of time) B) much better fitting clothes (like so tight you can barely stand up straight off the bike), and C) better tires and tubes (Corsa Speeds with latex tubes or some other such combination). Other things to improve speed come from a more aero helmet, maximizing pack/drafting skills, improving descending and cornering skills, and ensuring adequate nutrition to maintain maximum performance.

Potentially even more significant than any of that: just go ride more. 2-3x more. 2200 a year is a great start, but you should build significantly from there (and quickly) if you're serious about improving fitness/speed. No real shortcuts in endurance sports, aside from pure genetic talent. Gotta wear out those tires over and over again. At this point I'd wager that simply putting in more miles would get you more gains than intervals (though of course you can always incorporate those, too).