Actually you're not quite right about HDMI 1.3. The current spec HDMI (v1.2) supports upto 1080p @ 50/60 Hz with standard sound (can't remember if this goes upto dolby 5.1 or if it's just stereo).
This is what the curent Sony X series supports. Actually the current X series TVs were launched before the HDMI 1.3 standard was completed....so no chance of support anyway.
What HDMI 1.3 brings to the table is "high colour" and HD sound support.
High colour means that it wil support 10 or 12 bits of colour per pixel ....this is something that curent LCDs and plasmas don't support at a chip or panel level anyway and probably won't for a good while yet (read 12-18 months).
The HD sound is what you will get on the new HD DVD and BluRay discs .... I believe it's uncompressed high bit rate multi channel sound which your stereo tv will not be able to take advantage of anyway.....you would really need a decent AV amp to get any benifit from HD sound.
So as far as HDMI 1.3 goes, you don't need it for your TV as it won't make any difference. However if you're thinking of getting a HDDVD/BluRay player and an AV amp, you should make sure that these two bits of kit DO support HDMI 1.3 and it's probably worth holding off buying them until later this year when HDMI 1.3 should be more common.
Edit: ....typing too slow, sorry for echoing Neilo TM and neilmcl. HDMI is a bit of a specialist subject for me