This was something I considered as well many years ago, but chose not to do it.
There is always the time in type issue. But, having the rating can't hurt. Small operators or Part 135 operators might like to see this if they operate an aircraft you are typed in.
I chose not to do it because I was so current in the Duchess already from instructing in it, that I didn't need any additional training before the checkride. So I just had to pay for the rental and the examiner fee for the checkride. It was the least expensive Certificate I ever got!
A Citation is a very easy jet to fly. Only 2 levers to deal with, very simple systems, and landing speeds of 100 knots. It would be a relatively easy transition, at least if you are instrument current already. There are also a LOT of Citations out there that a CE-500 type rating would allow you to fly. Not that you would be allowed to just go out there and fly one, but you would at least be certified to do so. The models included in the CE-500 Type Rating include:
Citation 500
Citation I
Citation II
Citation SII
Citation Bravo
Citation V
Citation Ultra
Citation Ultra Encore
I wouldn't recommend doing it in a Lear. They are more difficult to fly and it would be harder to get through a quickie course in my opinion.
If the cost isn't an issue, I would say that it couldn't hurt. If you are on a tight budget, then forget about it! Also, it would give you some new experience. Just make sure you are real instrument proficient before you do the course. Some time in a Frasca ahead of time will be a lot cheaper than extra time in the Citation!
Good Luck,
JetPilot500