more great questions.
one i can answer pretty definitively, and depressingly
So in your opinion, can releasing something as donationware actually generate more funds than say a traditional pay-to-unlock model?
i'm sorry to say that my experience is that you will never make close to as much in donations as you would selling your software. that is the unfortunate conclusion i have come to after years involvement in donationcoder, which i think is probably one of the most "successful" (in terms of donations and users) donation-based software sites that there is.
however, this only takes into consideration financial gain -- for many of us there are other issues besides financial gain that outweigh the differences (see my old article here
Keep in mind that some people assume incorrectly that this site would be hostile to traditional shareware and commercial software but we are not, so no one will begrudge you trying to make money on your software. Though of course it won't come as a surprise that most of us here tend to be more interested in and curious about software that is free/donationware.
Now that said, here's a philosophical question for you: surely a "lite" version of a program that is completely free, but missing maybe some advanced features of a "pro" version, so long as it doesn't nag, would be considered free/donationware, correct? If so, does bundling two versions into the same installed product (in other words, upgrading to unlock certain features) also count as free/donationware, again so long as there is not any annoying nagging to upgrade? I ask this mainly because from a design standpoint it is much simpler to create a single product rather than two versions, one free and one pro.
another really good question -- framed very logically.
again you will find differences in opinion here. some people will view the lite version as primarily a marketing strategy and say it's no different than giving someone a feature-limited demo. it's really that gray line thing again, and it's mostly going to come down to what features you disable.
Obviously if you disable key features like the ability to save documents, then you are really talking about not a free version but a non-time-limited demo which people will have to upgrade to make any good use of the program.
On the other hand if the program is useful to large numbers of people without ever paying for pro features, and you aren't frequently nagging them to upgrade, then i think you can argue that you are talking about a free lite version and a pro pay version, which seems reasonable to me. You just have to be careful how you "advertise" it on your web page and in other places, to make sure people know what they are getting, etc.
Another model you haven't mentioned yet, which i find particularly attractive, and seems to be gaining in some popularity recently, is the "Free for Personal Use" model -- whereby there is really only one version of the program, which is free and does not nag the user or have any limits, but for which the license is allowed only for personal use (or as we do it here on donationcoder, free for personal and small/home office business type use). Commercial users are expected to pay for a license to use the software.
Whether you can make money with a "free for personal use" type license will depend very much on the kind of program, and i suspect on the kind of marketing you do. Some companies seem to do exceedingly well with such a model, but they tend to be pretty aggressive in marketing/selling their software to businesses. they get the benefit of free press from being a free program, and a good user base, and then they actively try to market the program to businesses. there are quite a few security programs that work on this model.