I'm not familiar with the HW2 or HST1 but some years ago when I had a Sony camcorder I tried the HGZ1:
http/store.sony.com/webapp/wcs/stores/servlet/StoreSearch?storeId=10151&langId=-1&catalogId=10551&in_dim_search=&Ntk=&Ntx=&Nrt=&Nrr=&Nrk=&Nrm=&keyword=ECM-HGZ1
I wasn't satisfied with the (slightly) improved sound quality. I also found the build-quality of the mic itself quite poor - very cheap and fragile. I don't know if the HW2 or HST1 are any different - maybe a little better. But I would be very reluctant to try either of them.
Also, the wireless HW2 is more suitable for doing interviews or the like. If you're filming something else... scenery, your children, etc... keep in mind you would always have to hold the mic, attach it to yourself somewhere, or attach it to your subject. It can easily pick up unwanted noise, be blocked, or if the mic turns to the side the whole sound profile changes. It's not really ideal for everyday, casual use.
My suggestion, stay away from the HW2 and HST1. I'm no expert, merely a photographer and shoot stock video from time to time using a DSLR and one of these Rode mics:
http/www.bhphotovideo.com/c/product/450170-REG/Rode_STEREO_VIDEOMIC_Stereo_VideoMic_Camera.html
The sound quality is quite good, but the mic would be a little big and heavy for a compact camcorder.
For your needs, maybe something like these:
http/www.bhphotovideo.com/c/product/444022-REG/Azden_SMX_10_SMX_10_Stereo_Microphone.html
http
/www.amazon.com/Audio-Technica-PRO24CM-Stereo-Microphone-Camera/dp/B0016ARZ9C/ref=sr_1_21?ie=UTF8&qid=1336776010&sr=8-21
I'm sure there are many other, perhaps more suitable and/or better ones... above are just to give an idea of size. Maybe you can find a dedicated forum for Sony camcorders and seek additional advice or recommendations there. The mic adapters may be more difficult to find in a local store, but maybe you could purchase an adapter online, and take your camera to a store to test 2-3 different mics.