180 gram vinyl vs First Pressing used

It’s true that there have always been defects in mass produced vinyl.
But when the golden age of vinyl ended, pressing plants closed, lathes and all associated equipment were liquidated and the craftsmen who manufactured these records lost their jobs.

Since the resurgence of vinyl, there is, for the most part, a new generation of cutters and pressing technicians.
Also the business of pressing records contained many new startups. The demand for vinyl has stressed these companies to their limit and, IMO, there has been poor quality control.

Just read the many forums which contain threads about defects in newly produced vinyl. There can be vast differences in the quality of the product between different manufacturers.
The defects go beyond pops or noise from the vinyl. A common defect is warped or dished records.

As millercarbon alluded to, 180g has nothing to do with the quality of records being produced. It's simply the current product being produced vs. 120 gram and 150g in past years.

I'm listening to Van Halen's first album on 180 gram vinyl right now and it's sounding better than ever. I've heard good and bad 180 gram pressings and the same goes for 120 gram pressings. I will agree that many new pressings in general seem to have a lot of defects. 

The weight of a vinyl does not refer to SQ, it is just marketing hype and actually nonsense. The mastering and manufacturing process alone matters. So a 180 gram reissue can sound good or bad, usually they have been OK, IME. But I always prefer the early pressing and try to avoid these modern heavy editions.
Of course there are exceptions, like this "Smokin´ " by Humble Pie: Analogue Productions APP 4342. So, in this case the early editions are the real life humble pies : )
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&...

They can be great and they can be awful. There are many small companies that are reliably great like Friday Music and Analog Productions. Then there are companies that are reliably awful like Rycodisc. Back in the old days BCD it broke down in genres. Classical routinely great, popular music routinely bad and Jazz label dependent. 
I would certainly rather have a good 130 gm record than a bad 180 gm record. I think record weight is more of a marketing tool than anything. 
The best of today's quality is just as good if not better than the old days. I do not think there is anything special about old pressings and most of the remasters I have are distinctly better than the originals. Frank Zappa's early discs are a great example. My original copy of  We Are Only In It For The Money is very bass shy but the remaster is perfectly balanced and much punchier. It has to do with the systems the mastering engineers were listening too. I would bet Frank's system was over boosted in the bass consequently the original master is bass shy. Same for David Bowie's early recordings The remaster of The Man that Sold the World you wouldn't believe is the same record. The original master was awful. Anything on Rycodisc you are better off going digital. I have an idea for a thread.