That's not how it works although it sounds good in theory. Any money collected from fines would go to "general revenue". If C&P would find ways to save money they would likely not see a big increase in their budget. It means they can do with less. The Feds are in deficit reduction so any cost savings is going somewhere else and not to the ground forces....well maybe at election time.
They do undercover work but it's not all done by hiding behind trees or looking like some angler. Investigative work includes gathering information through emails, texts, social media and the internet in general.
Oh, I know it isn't how it works but that doesn't mean it isn't how it should work. Granted, it might lead to ticket happy officers so that they can pad their budget.
Or, better yet, ticket money goes into habitat enhancement projects, education classes, hatcheries, etc.
And sure, they might do some undercover work without being out on the river, but seeing how some of these people are fishing, you aren't going to know this unless you are out there. Unless it is reported, somebody isn't going to post on facebook pictures of them snagging fish unless they are really dumb.