Multi Chancel NMEA logger (to SD-Card). Arduino? MK808? RasberryPI?

Over the years i installed several equipment into my car that need GPS-Data.
Most of those applicances just integrated an NMEA-module which in principle could work stand-alone.
the serial data (RS232) in TTL/CMOS/V.24 can be found inside these PNAs etc.
Just the baudrate used differes (from 4800 up to 115200) some of the boxes like to speak to “their” module to (un)set static navitation.

What i would like to have is some kind of arduino-shield or bank of Profilic USB/RS232 hooked to an usb-up, hooked to a MK802/808 android device.
There connect all available gps sources. (at the moment: dashboard cam, WinCE PDA, WinCE PNA, Naviceiver)
Why? Because they do offer different results and i can not say “one is totally better than the other”, it’s just differend chipsets. one works better in urban “canyons”, others more precise on slow speeds, others on hefty skew rates and/or drastic accellerations (going slalom in valey with vector systematically above 0.5g)

Storage should be a FAT32 SD-Card.
And if totally advanced, a button to connect via BT to a mobile phone and use it’s teathering to upload to dropbox or just FTP…

But a definite must: Some power down procedure to shutdown safe when the car’s supply is cut off.

Maybe there is already a (partly) solution.