i think someone would have to really know their stuff to look for a power sounder on the Omega, if you have a smash, are they really going to try and get the scuttle off to check its there? :-/
If its nicked, you won't be getting it back anyway. Removal is the best option IMO.
Omegas are worthless and no one wants to steal them, if scumbag wants to get to his crack house, he will steal a 1995 Fiesta, much easier.
If a second scumbag wants to steal to sell on, no way will he pick an Omega, he will go next door for that BMW. 
Insurance assessors can be a PITA
Cut off the lead for the sounder at the base of the loom, seal with black insulating tape. No one will notice, if you have a front or rear end smash they are not going to be interested in the alarm.
But, like I said, there should be something in there, other than a piece of charred metal or a rather big hole.
Its the scuttle drain, its mean to be a hole!

I give up with you. I think there's a rather hole between your ears sometimes. I have a very good memory, and if you care to trawl back a few years, you'll find that I was one of the first to post about this problem, and you were one of the first to follow up on the advice given. All of a sudden, you're the expert.
This was about the time when people were explaining to you what an engine was.