One of the advamtages of sniper strike teams is their price. They are very cheap. Adding an upgrade worth 10 points might not be that great idea. As for the list building as mentioned above start with the commander. I'm playing vader. Hes got courage ,,-" so basicly trooper units are great with him so my whole army consists of them. So adding stormtroopers with dlt's as the main force. Next up: heavy hitters, things that deal damage. Boba Fett is great at dealing damage and beeing anoying. Scout trooper squad is also stron but fragile. Snowtroopers ca also deal a lot of damage with flaethrower and nades. Next: matchups. Do i have an answer to armor, to infantry to heroes. If not add one. Boba is great at taking down infantry, same for snipers and 4 man scout squads but my anti tank capabilities lack a bit (1 impact on boba dlts and some more on vader) so ive added hh12 launcher with impact and long range. In order to make my 2 heroes work i need upgrades on them. And thats my pretty balanced competitve list with 8 activations.
What makes a good list?
To make a good list I suggest a couple of things:
1. Have 8+ activations, one of the reasons people want more activations is to try and keep a couple high value units in reserve and move them last so that they don't take fire.
2. Have a suppression remover, such as Leia or Veers. The new generic commanders will help here.
3. Have at least one unit who can wipe out a unit in one attack. Basically depending on terrain, force composition, etc. someone will make a mistake, and you need to punish that play for it when it occurs. Luke, Boba, ATST, Fleet Troopers, Snow troopers with a flamer.
4. Plan for trooper spam first and vehicles second. Vehicles can often be played around, but trooper spam really can't. For instance I often see a player put impact grenades on almost all their troopers which is a mistake. You should put it on a couple of troopers and then deploy smartly and protect them until needed, if needed.
5. Understand what your list does well and what you will have problems with. This is critical because when you are defining the battlefield and choosing objectives you can seriously hamper yourself or your opponent.