Two suggestions: 1) You don't need to make it lengthy 2) Keep it as objective as possible. Don't hand out 10's for a $100 uke - that's just not realistic.
I totally agree that we should all be posting more reviews.
HOWEVER-- I think that your demand for objectivity is misplaced. Frankly, reviews are inherently subjective. They're assessments of your opinion of the object in question.
An "objective" review would consist of measurements, materials, and maybe some sonic spectrum analysis or something if the reviewer had the tools available to them. Anything much more than that becomes, quite quickly, subjective.
Moreover, I think you're kind of off on your conflation of price with quality. Should reviews consist of, essentially, "This is a one thousand dollar uke, therefore it is good," or "this is a one hundred dollar uke, and one hundred dollars gets you four stars?"
Which deserves a higher ranking-- a one hundred dollar uke that sounds good and is well set up, or a five hundred dollar uke that doesn't sound much better? Personally, I'd prefer the former. I'm more interested in value than I am in purchasing a status symbol.
I think that some of the "unrealistic" reviews you're thinking of consist of the reviewer weighing value, expectations, and overall satisfaction. A cheap uke that plays well is going to make people happier than an expensive instrument that doesn't live up to its price point.
Or to put it another way: think of it like grading. If you get an "A" on a paper, that doesn't mean that the paper is perfect. Far from it. It just means that the paper met or surpassed the expectations of the instructor for the assignment. And you don't get graded to the same standard in second grade as you do in college.
Likewise, as people pay more for a ukulele, they expect more. The worst five hundred dollar solid wood uke might still sound better than the best hundred dollar laminate, (though I personally doubt that's the case) but they shouldn't be evaluated by the same standard. The person who got the worst five hundred dollar uke on the market still has reason to be dissatisfied, and the person who got the best hundred dollar uke on the market has every reason to be pleased.
Honestly, I think the second person has more reason to give a 10 to his instrument than the first guy. I think the first guy just got bilked.
While bigger prices tend to come with better ukes, one shouldn't assume that they're the same thing. To do so is kind of snobish, to my mind, and not really in keeping with the spirit of this community.