accelerometer accuracy determination
No it doesn't work like that. Firstly you are using 9.81 in your equation and this is the gravitional force exerted by the earth on mass. This has nothing to do with measuring g-forces when a body is accelerating due to it spinning (for instance).

Secondly, the noise floor, I believe is the total noise produced across the full range of frequencies (1 Hz to 20 kHz) that the accelerometer can work with and can't be simply used to compare the signal you might get from say accelerating at a constant g in one direction or the other.

Thirdly, your question has the word "accuracy" and I think your calculations were aimed at measuring resolution - these are different things. For instance a 12-bit DAC has a resolution that is one in 4096 but it's accuracy may only be 1% - accuracy and resolution are not usually interchangeable.

If you had an experiment to determine the g-force on an object spinning at say 100 revs per second, you know that the frequency of the signal will be 100 Hz and you can apply filters to extract this signal and counteract the 35 uV broadband noise. 

35 uV with a 20kHz bandwidth is about 247 nV per \$\sqrt{Hz}\$ and so if your filter has a dc to 200Hz bandwidth, the noise will be 3.5 uV. This is a lot different to comparing it with 35 uV.