Should you reseed your pasture? 

The weeds will hold the soil, that is why they are there. This is not pasture, or very poor pasture so it is dormant ground with ground cover. Spend $O.00 on it.

Would you recommend put amendments to a area to promote more growth of perennial grasses. Maybe plugging it. I live in the high country of new Mexico. Looking for a cost effective way of increase grass cover . To stop erosion. Do these methods work in a pasture as well as the do a yard. And in dry area like mine?

A lot of those so-called "weeds" have deep taproots that help with water infiltration and provide biodiversity.

If not using it for Pasture why care if it has weeds or not? Alot of things people might call weeds can actually be useful. Now if wanted for Pasture unroll some hay for a day and let some cattle or sheep fertilize it. If really worried, some people will overseed and let the livestock trample the seed into the ground. But if good quality hay is used, that might not even be needed.

round up Monsanto production!

Bindweed! Dump the place and run to some other continent!

OR You could run cattle through there once maybe twice a year for one day only on any given paddock and make a profit on the weight gain.and restore the grass at the same time. ;-) Allan Savory: How to green the world's deserts and reverse climate change

Lost me at Roundup