I found the new version of imagevue ( X2.8 ) much, much more SEO friendly than previously.
In my case, I can easily find a lot of my images in google on the first place, typing a single quote (short name of image subject).
I think all of this depends on type of content and subject in general.
In your example - flowers - on the web is a bilion of flower images existing for a long time. Google will show first images that are mostly viewed. And not viewed precisely as image, but as page that contains that image. Therefore most popular pages get more search results in images.
Guess what - even if some really popular web page/service shows only cars and for some reason they put online a single image of an flower, they will get more search results for that flower than site which contains a hundreds images of the same flower but have only a few views daily. Even for a car name thy can get this image as a search relult
(google search rank == image search rank).
Popular web pages (most of them use kinda "SEO boosters") get 1.ooo's views every day . I guess your site don't gets as much traffic, that's why don't generates many search results.
The search bots don't sit on one page waiting for a feedback from user

They "walk" around the links on the web. From one site to another. If the bot visit to your site frequently it thinks that your site is important and will rate it higher for a certain keyword.