This is a conversation we have often at work. My company often travels full teams with their gear. It takes us a long time to trust new vendors. So if it's a new city to us we will send a tried and true crew. Our sales team is not a fan. In addition to the cost sometimes there is increased risk. Such as vendors renting equipment in the destination city and that rental not being up to par, or not being able to run to the shop if something is missing. We do live broadcasts so that environment can be much less flexible then other types of field production. I've never regretted standing by a crew we trust.
Mike - Your inquiry is not a simple question to answer. There are a lot of variables to consider when joining the Guild. If your life long end goal is to become an ASC member than the answer is simple, yes, join the guild. The members of IATSE are well trained individuals who have access to all the latest equipment, work flows, and yes, set protocol. I don't know your main genre of expertise in the Motion Picture Industry but if your a Reality TV DP there's not much sense in joining the guild as most productions in this genre are non union. The other question to ask yourself is who do I know in the union. It is truly a "who do you know" business we work in. Those people will pass you along from show to show, but if you don't know them there not going to hire you. If your a commercial DP it kind of makes sense as most Nation Campaigns are union... and pay accordingly.
I work in most areas of the business. I learned a lot as an IATSE member. Keep this in mind, if you primarily work in areas of our business that are non union than it doesn't make much sense.
In order to get Health Insurance through the Union you need to work 350 hrs in a 6 month period. This means you need to DP or Operate an Episodic doing your 70 to 80 hour weeks for the duration of the show or at least get on a Feature for a 3 to 4 month run.
Other things to take it to consideration are age and current financial obligations like Mortgage, Kids, etc. You may need to take two steps back before moving forward if you join the Guild. For me it was/is worth it. If you'd like to chat further please feel free to contact me off list. Good Luck