No one can tell you how to vote
Voting is a very subjective thing. Some people are liberal, others not so much. Ultimately, you should upvote or downvote an answer (or question) if you think it's deserving of that vote.
This faq post on Mother Meta is a very similar question, asking when should you vote. The accepted answer says
I generally use "does the post help the site?" to judge upvotes and downvotes to some extent.
which I personally think is a good criteria for voting. Golfed answers (or more generally, answers that have improved their score) certainly help the site, after all, that's what we're all here for. On the flip side however, there are certainly users that golf before they post, not after (myself often included), and so only voting up answers with demonstrated golfing may not be the best idea.
Ultimately, if you think it deserves an upvote, give it an upvote. If you think it should be downvoted, downvote. If neither, do neither.
Note: people will be constantly improving their submissions from the moment they get a working program to the point where they (and others) sit back and believe it's an optimal solution. Sometimes you'll see these improvements, sometimes you won't, which is why (IMO) you shouldn't vote just because an answer has struck-through scores. If, however, you want to, no one's going to stop you