Why would 20k be a bad thing? Sure, you take a hit to your economy, but only until you get back down to 20k. If the hit makes you lose money, just blow the excess instantly on something.
George Simpson. I was agreeing with your post until i read GW Swicord's answer. I just want to add something to what he said because it took me two reads to understand. When you get the 1000 bc anomoly it is between turns. So, if you werea at anything above 19,000 at the end of your turn, that boost will put you over the top for the whole turn, costing you tens of thousands of BC or more. you will not have the ability to spend it off until your next turn begins, which by the its too late. I know, I know, then just keep your treasury below 19,000bc.
I have like 3 surveyors on my large maps and they all stay on auto-survey.
A nice little fact: The AI races will not build additional survey ships and will not replace their flag ship if it is destroyed. So, late game, yours may be they onl;y ones in the galaxy.
The respawing of anomolies gave some credance to building the Galactic Guide Book, which allows all ships to survey. That is, the survey module will have a size and/or cost (?? not sure) of zero bc. You will still need to have ships designed with the module. Personally i still have never build that thing.
As for wormholes... on other bit of information. It is likely, especially on larger maps, that after going through one your ship will not have the life support it needs to be where it is and you will have to head back toward you own space. This makes your survey ship useless for a few turns, untill it gets close enough to your space.