Good sniping spots in Dust Plains are on the cliff and on top of the downed Techno Union Ship.
There are three good sniping spots in Spire:
1. Play as the Republic and choose the Clone Sharpshooter. Get in a LAAT Gunship and fly over to the Techno Union Ships. Try to land on the very edge of the ships. Get out of the gunship and you can snipe droids as they spawn from the ships. You can also reach other enemy command posts.
2. Play as the Republic and choose the Clone Sharpshooter. Get in a LAAT Gunship and land on top of the CIS's main command post. You can get a good view of the battlefield from there.
3. Play as the CIS and spawn at the main command post, where you can get in the speeders that Count Dooku used to escape. Get in a speeder and land behind the Republic's command post that has the LAAT Gunships. You can snipe the clones as they spawn there. You can also reach the other Republic command post from that spot.