a) the infomerical producer wants to add some fluff to my program so they can increase the price at least 3 to 4 times more than what it goes for on the web... to me this just doesn't seem right.
It's actually not fluff. A good book on making money from infomercials is "A Millionaire's Notebook" by Steven K Scott. In it he says there is a minimum price for any product that is sold on TV... that's why you never see any product below this price-point because of the economics of this type of advertising.
Seriously, I'd consider taking this offer if the infomercial producer is reputable (double/triple-check first - a must!) You have an extremely popular subject with diet plans, and plenty of potential yet.
And I don't think these sales will impact on your net business because you reach a far wider - and different - market through television.
b) the book publisher wants to give me a substantial amount of money up front... however this would not be added to at all UNTIL they recoup their own investment... then once that happens, we'll split the profits... but certainly not even! I'll be lucky to garner 15% to 25% of each book sold. Once my book is in the stores... there's the possibility that the eBook I sell on the web could lose sales dramatically... not something I want to experience right now.
The publisher's advance and conditions is quite in order - this is what happens with all authors. However, if you think you might get 15% back, this figure may be high... many of my offline sources put this amount more around 5-10%.
Still, with the possible exception of having to do promos (booksignings, commercials etc), that's still a lot of income for no work and a wider area of exposure.
I wouldn't worry about it clashing with your net income - as long as you keep the product consistant so that existing hardcopy buyers don't mistakenly double-buy your online manual.
My advice - go for all avenues of revenue! You may not get this opportunity again.