Just wondered if I can be of help.
I already have a tracking software developed that could be changed to collect the data your after. It already works by internet or wifi and works on an sqllite database.
I found out alot about nmea strings on this site. Hugely helpful.
One of the key things I found out about was accuracy. Each nmea string has its own variable of how accurate it is so its easy to set a level of accuracy to consider worth collecting or not.
anyway if you need me I'm here and interested.