よいXを is an expression you can find in many other cases. Mostly with 年 and 旅 . It should be followed by 祈ります or something on the same line, meaning I pray/hope that you have a good X.
Here most certainly it is よい夢を見て下さい, I mean, this is what the sentence means, but the usage of yoi makes dropping the verb more natural. If you want to use the verb, いい夢を見て下さい is probably more frequently used.
Ending the sentence at the postposition is perfectly fine with a lot a postpositions, and it's particularly frequent in written language (a lot of advertisements uses this style).
I pray you will have よい旅を。よい年を。御運を。
Let's go toward よい明日へ。 (not literally: a good future/a better tomorrow)
I'll wait/Stay well また会う日まで
Sometimes it happens in the middle of a sentence.
お元気で(いて)ね is an example.
This is a sign I've seen on the net:
Actually you can drop postpositions too:
(The inversion of topic/subject/object with a verb is another interesting phenomenon.)
However you can't do anything like this if it's not obvious for you and the listener what's the verb the should follow: it MUST be clear from context. So if you say よい夢へ it's not clear what you mean, you can't just end it with へ because is convenient, it needs to make sense in the context.
If you find the answer unsatisfactory please post a comment instead of just downvoting.