After the events of T1 Skynet was built much faster thanks to the severed hand of T-800. After realizing this, why didn't Skynet send more data/material into the past and make itself stronger rather then trying to kill the Connor family?
The Butterfly Effect states that the smallest change to an environment can have massive ramifications.
So, why did Skynet start mucking about with the timeline in the first place? Because it had lost, and it was desperate
In Terminator 1984 Kyle Reese says
It had no choice. Their defense grid was smashed. We'd won
The danger involved in sending back resources to make itself stronger are far too great. Due to chaos theory (butterfly effect) Skynet could inadvertently cause itself not to be created. It has a better chance of killing a nobody (Sarah/John) in the past and not affecting its own creation, as they don't become important until after Judgement Day
Skynet wants to research better terminators? Well that takes some trial and error so at the end of 24 hours, send the best designs along with a record back 24 hours and work from there, get 10,000 years worth of research done in 24 hours.
Ditto with battles with the resistance. Resistance wins a battle? Send back details a few days and make sure there's land mines just where they were planning to send their main attack.
It's probably one of those things you have to chalk up to the writers not wanting to make the enemy too overpowered. Skynet using time travel to full effect is just too tough an enemy if the resistance don't have their own time machines and too confusing if they do.