If what you have written is a simple, broad-stroked and more or less stereotypical tale which is grammatically correct and devoid of typos but nothing more than that, and your cover emanates an aura of advanced literary genius, promising complex and layered writing, you should be ready to be judged accordingly.
I find it difficult to believe that it is not possible for a writer to understand what kind of cover his or her novel deserves. And even if I'm wrong... even if there is a writer out there who claims to not have what it takes to match the level of his writing with a picture he's going to wrap his writing using, I'd say, why not go for a simple cover?
Two examples I can give here of excellent covers that do not deceive the readers in any way are below:
1. The Joke- Milan Kundera
Yes, it is hideously deceiving, but only in the sense that Kundera's writing is as beautiful as the cover is ugly. Yet, you keep going back to the cover and take comfort in its simplicity as the author narrates his heavy-on-philosophy story about a political ideology gone wrong and the pointlessness of delayed revenge.
2. Twice Written- K. Sridhar
I bought this book just because the cover caught my attention. I knew nothing about the author when I did. And while I may not have a rave review to offer overall (some scenes are powerful and excellently done, the rest is very good but nothing beyond that), the level of writing in this was actually as layered as the cover made me anticipate it to be. Whether good or bad is a different question altogether. My point here is, after finishing the book I did not feel deceived.
In my opinion, a fancy cover does more harm than help- that is if you're aiming higher than selling your first two hundred copies.
Ditto for blurbs.
Disclaimer: The post may well not apply to cases where the author has had no real say in the making of the cover and the blurb.