You stated that you are just looking for a replacement...I provided 3 motherboards that appear to be available that are in consonance with the hardware that you currently employ.
It's unrealistic (in my view) to speak of boards which are fading fast as far as consumer presence go...in terms like "lateral" or "upgrade." They are a vanishing breed and these are just some of the vanishing breed that happened to be available as of yesterday.
Nobody is making 478-pin boards these days, so you have to pretty much take what is available from vendors who happened to have 478-pin boards in their inventories.
Or take a chance on buying a used board via eBay.
You can compare the specs and determine if those boards are better than your current board...it's your decision.
Me...I always prefer a working system to a nonworking system