Adding seats doesn't increase atmosphere. A fully finished stand, either all safe standing or all seating, will look a much more professional attractive proposition (although personally I don't think the current stand / ground turns people away nor do I think a new stand will necessarily attract people).
What I'm really struggling with is to see how a half and half stand like you have suggested will look anything other than tin pot, that's why I asked for examples of other stands so I can see what it would look like.
Firstly its not important to have an exact copy of some other clubs ground, infact you hear a lot of fans not liking visiting identy kit or lego esque stadium such as little sixfields, so it doesnt sell its self well. Some originality would likely attract more visiting fans.
I suggested a new 12 row extention behind both goals that are a safe terracing, many fans mainly older wish to remain seated so need catering for, so leaving what is there in situ makes perfect financial sense.
This way gives the ground a professional outlook and feel with a far greater atmosphere that will in turn attract more supporters and increases capacity to above the much needed 12000.
The funding of this would still require getting in some investment, sponsorship, long term multiple ticket sales and most importantly the full support and help of our catchment makes this very acheivable .
Doing nothing for another 20 years isnt an option any more.