What are my old BM's worth? Any 6er Gran Coupe issues to note?

I've had my head turned by a new car (6 series Gran Coupe) and can't shake the want. I don't do a whole pile of mileage, maybe 7,000km per year, and currently drive an E92 325i MSport Coupe. It's 2008, in very good condition, has the cheaper tax (3.0 6cylinder petrol for about €600 p/y), just ticked over 160k km, full leather & auto and is well maintained.

I also have an 2002 E46 318ci MSport Coupe that has been parked up indoors and under covers for a few years. Also in very good condition, blue, factory MSport, Alcantara interior and approx 135k miles.

I had intended packing up the 325i alongside the E46 but as time moves on I'm starting to realise I'm unlikely to do much with them into the future. This realisation hit me when my partner's dad offered me a waterlogged 628CSi that rusted to basically nothing in his back garden due to it always being on the long finger!

So, what are they worth these days and am I making a mistake in flogging them to fund a (probably small) portion of the bigger car?

Thanks!