Google has been doing this for a while.

Sometimes they add your URL to the end of a title tag.

I have some title tags that are short but have my URL at the end.  Google is adding my URL on top of that.  Looks like this.....

Keywords at Egols.com | egols.com

Sometimes they replace your title tag with words that  match the querry.

I object to this because they have overwritten a title tag that with my marketing message such as "free shipping" or a kickass price that pulls in buyers.

I always use a 301 redirect.

2K is a lot of pages.  If I can redirect them with a couple lines of htaccess code I would do it.  If I had to code 2K lines and have that huge file scanned for thousands of visitors I might not do it if I am pretty sure that there is very little traffic.

I use lots of folders on my site and that makes these problems easy to solve.

Suppose you are not sure of what keywords you want to rank for but just want to see a list of phrases that have 500-5000 searches a day, low cost and low competition because you are looking for phrases that interest you for which it will be easier to rank close to #1 in google.

I think that most of these "mouse holes" have been discovered and are now occupied. 

You might find one but I think that you will discover... is when competition is easy and the cost is low there is a really good reason for that.