Ok, so Akitaro Watanabe is clearly an Economy card, and as such, how much money he makes/saves you must be compared to the output of other cards that you might play instead of him.
1 Ice Rezzed: +1, but since it cost a to install, you might as well have clicked for a credit.
2 Ice Rezzed: +3, like a Beanstalk Royalties that requires an extra credit to fire.
3 Ice Rezzed: +5, now installing him is comparable to a Restructure, that has the cost to play spread out over the ice you've rezzed.
4 Ice Rezzed: +7, this is starting to get ridiculous, but at this point you must have spent 6 just installing ice protecting this server, which must be considered.
On top of the comparison to economy operations, you must of course consider that the runner may choose to trash him, which though it may stop you from lowering the cost of more ice, the cost to the runner must be accounted for as well.
Unfortunately, as optimistic as the above analysis might start looking, you have to consider that he is only really that useful if drawn early in the game, before you've rezzed most of your ice, whereas economy operations can still be useful as the game progresses. Furthermore, if you have a full 3 copies in your deck, to ensure that you draw him early; then the other copies in your deck that are drawn late, are still effectively useless.
Though in theory Akitaro Watanabe could save you quite a lot of credits, he is difficult to make good use of.
Perhaps once there are enough good Sysops for Jinteki's Recruiting Trip to be useful, Akitaro will have his day, but until then, you're probably better off with a PAD Campaign, or perhaps even a Medical Research Fundraiser.