ALWAYS RESPOND TO RECRUITERS (unless it's clearly a pyramid scheme)!
1. You may not need their support right now, but things could change for you at any time. Build a relationship now.
2. You risk losing the connection for good if you don't respond and leave them with a positive impression.
3. They may not be presenting you with an opportunity of interest, but you can share your interests so they can be on the lookout for relevant opportunities.
4. It's free for you as the job seeker. Or should be - if it's not - don't engage.