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The BD30 does not internally decode TrueHD or DTS-HD High Resolution which the BD10 does. Also the BD10 plays DVD-Audio which the BD30 doesn't, and got better reviews for its normal DVD playback. So assuming that your BD10 is attached to your surround amp via 5.1 analogues, then for now the BD10 remains a good player. It's only downside I would say is its speed of operation.
To get something that offers more features than your BD10 with your current setup means waiting for the Panasonic BD50, Pioneer LX51, Sony BDP-S550, and then there is no gaurantee that they will better the quality of the BD10, just that they will offer DTS-HD MA decoding and faster operation.
I would replace the Sony surround first personally. It will allow you to get the best out of your existing BD10 and XA1, and the only things you'll be missing out on are DTS-HD MA, which probably isn't that big a loss on HD-DVD, and profile 1.1 support on Blu-ray, which equally isn't much of a loss at present either given how few discs there are...
If you get the BD30 first, you'll lose TrueHD on Blu-ray support which given the growing no. of discs that have it may be a problem and you still won't have DTS-HD MA anyway.
By the time you've upgraded your amp, and had some time to enjoy the better sound that gives, hopefully we'll have more choice of Profile 1.1+ players which may suit you better and may also lead to better pricing due to some competition for the Panasonic. There's a growing list of players due by the end of the year, but none of them are much good without the amp upgrade IMO.