My take on this, as I am just starting to understand and want to race.
It's like a company, take care of the employees and the employees will take care of the company. So, the vast majority need to be factored into this topic with fairness and understanding that some have honest intent to move up and other don't care and want to just take up space.
But where do I fall into this. I want to ride, but to poor to race a full series. So am I limited to the Sportsmans class where weekend warriors run away with all the local events or do I just focus on the final standing and just go with the flow.
I think I will just look at final standings, not class structure and see how I place in final standings as a motivational factor to me. This is how I went from a nobody "Redneck" with a bow to a National and World competitor in the Olympic Archery sport.
This year was my first year racing as well and here is my take on it.
Go race your own race and only gauge your results against yourself, my opinion is that your first and probably second year at any particular event or series is for learning.
There is so much to learn: how the format works, what the course is like, where you can go fast with little risk, where it is better to dial it back, where does your bike setup provide an advantage, where do your skills provide an advantage, do you need to spend energy trying to pass a particular rider or is he going to wad it up in three corners riding over his head so save your energy?
The smart folks who have been racing the series year after year already know a lot of this. Given all that, actual placings and standings for your first season are basically throw away. If you get some knowledge but leave some trophies it's all good!
As to what class? Pick whichever one you think suits you and will let you pick up on things quickest.
I wouldn't worry about sandbaggers or any of that as you will have enough on your plate and things are different so much from race to race and series to series.
I personally jumped right to 30A, mainly so I could go off the line with my buds and ride the longer race with the harder course (C & sometimes B get different race times and courses in my series). So far I haven't DNF'ed or been DFL but reaching the middle of the pack consistently on my row will be an accomplishment.
There are guys on the 30A and 40A rows who make the top 5 overall regularly, but where are they going to move up to? Pro? Most of them have already been there and have other priorities now. When I get stomped in my class by dudes who are a few seconds off pro laps the only thing I feel is gratitude for being able to follow them for as long as possible and watch their lines and technique.
Looking at the overalls though I've consistently been at the top of the mid-pack and am very happy with that for my first season. Another thing to be happy about is if you can post up consistent laps or recover well from a crash or mechanical. There are plenty of small victories to celebrate on your way to moving up in the ranks and earning trophies.
Also, it sounds like you aren't wholly familiar with your bike and plan on switching some time in the near future, I'd expect to back slide a little bit then even if your new bike is better. Same goes for any major change really.
I think in the end it's all good and I'm super thankful to take part in a well run series (non AMA) that is affordable and has a great promoter. When it comes down to it grassroots off road racing is some of the most affordable racing there is and the people are the salt of the earth.
It's like having a second family you see every couple of weeks and gives you motivation to hone your skills beyond what trail riding might.