Don't see why they would be going up, when hardly anyone wants them. I have chucked a few boot loads of Omega parts in a skip because I couldn't give them away.
The thing is there is still enough of us who cherish our Omega's to make holding and selling of parts still a lucrative business. The main dealers only have a few parts left, and they have gone up in price considerably over the last 3 years. Now the parts that become available via the breakers, and there are pages and pages of them on the internet, are worth far more than they were worth when the main dealers had plentiful stocks of new ex-factory items. So the market forces of supply and demand rule and mean that if you have any Omega parts they will be worth a good, reasonable price . 
That's what eventually happens, but we're a long way from it. It is niche sites like this that make it look more viable than it really is.
These cars are still common, but even a good one isn't worth enough to be desirable. They don't suffer from major mechanical failures(the low price of a good automatic gearbox is a fine indicator - getting one for a similar age BMW or Mercedes was always costly because they were in demand), and all of the service/maintenance parts(filters, plugs, belts, water pumps, brakes etc) plus the long term wear parts(shocks, springs, bushes, radiators, gaskets, bearings)are readily available new at sensible prices. Garages won't buy these parts used, and it's pretty daft to do so for DIY work.
That only leaves trim, bolt on panels, the odd electrical part and the few upgrades that only apply to low spec cars for people breaking cars. This is a small market, with small returns even if you have the space and willingness to store a load of stuff long term.
The prices of used parts won't increase until
they and the cars that require them are both rare and expensive; which is unlikely to ever happen - just look at the low value of an early Senator.
