So HN already does this and it does it exactly the right way: if you submit something which already exists, it upvotes it instead of resubmitting it, which is exactly what you want.
If you want to submit a link (or upvote it) anyway, what is the added value of this bookmarklet?
The value is IMHO that you can access the comments of an existing entry within 2 clicks. Actually that's why I wrote this thing and how I use it personally. Found an interesting GitHub project? See what Hacker News says about it.
This saves me the time of heading over to HN and writing a competent title, only to realize it was submitted 340 days ago!
On the other hand, HN won't tell you it's a resubmit if the story isn't in memory (or in some cache? I'm not sure of the details) so it's still possible to submit a dupe. Submitting a link or searching on hnsearch.com is pretty cumbersome just to check if something's been submitted already.
Who wants to copy and paste a link into the submit page on hacker news, then get the message that it already exists when they can click this little bookmarklet.
I like it, good job!
Or just use the bookmarklet from the submit page...
Yeah, that works too, but this bookmarklet adds onto that by not only submitting it, but also takes you to the comments in case it already exists.
It's like saying "why use powered windows, when hand cranks work just fine"