In general, how you dress does reflect how you are treated. It can be bad, it can be good. Going higher than the minimimum can cut both ways, in my experience.
Here's a few cases:
To Be a Boss, Dress like the Boss
It even comes up on career sites. At a certain level, dressing to impresss does work. If you want to be a boss, look like a boss. Chances are, management hasn't sat down with HR to figure out a "Middle Manager Dress Code", but look around and see if even in a "business casual" office, the managers don't dress up a bit. It's probably not just that they needed a place to spend that extra dough - it's a type of branding.
Several times I've seen collegues get somewhere with this strategy. They had done the other hard work - training, experience, attention to people skills, etc. - the dressing up was just icing. But it made the boss go "hey, that guy looks spiffy today... hm... and he's been really on his game, I wonder if he'd be a good fit for the new X opportunity".
Are you interviewing?
Thank you to FrustratedWithFormsDesigner for the reminder! In a casual environment where the business situation is in rough shape, random dressing up is usually taken to mean that the employee is going on interviews. Most people (at least in the US) like to keep this information somewhat private, so my trick has always been to have a jacket and anything else that ups my game at the interview stashed in my bag or my car and I glam up before getting to the interview.
Ah! You're Dressed up, You Must be in Marketing!!
Seriously, this happened to me, but I bet it's happened to many engineers. Early in my career (ie, I was a very junior, independant contributor), I dressed up quite nicely because I am a girly girl and I had previously worked in a demo lab where uptight business casual was the norm (khakis, polo shirts, jackets on hand at all times), but in the new lab, it was low-end business casual (jeans w/out holes or fading, nice T-shirts, no jackets). Every day for months I came in dressed the old way, complete with up-do hair and makeup and no one spoke to me.
They all figured I was from the marketing group in the next cube block (who I sat near) and not the new engineering associate.
I had a bad dressing day (late night) - no makeup, no hair, no jacket - and suddently everyone was asking "hi! Are you new? Need a hand with the custom XYZ system?"
I learned my lesson. The jackets hung in my closet for another 5 years.
Working in the defense industry, I've seen a certain type of "group branding" that is not a status thing as much as a "I'm of this sub-culture thing". I've seen in many offices that groups of similar background or skill set seem to dress alike - there's a certain look to:
- Those who were in the military
- Those who lean towards long-haired hippie
- New age feminists and old-school feminists
And many others.
When I read the question, I tend to think that this is what you describe. Your new group that seems to have odd status use an intuitive dress code that says the "we're from the old company". It works for them, because they fit what the boss is used to, and it lets them self-identify.
You have the option of changing your own dress, to see if you can join the pack. Or you can try to just get to know them and see if you even want "in". Can't say that it'll make a difference. In one old company, there was a certain "cred" from having followed a certain career path, as a group had known each other for a long time, and had a lot of trust and respect for others who had shared their history. We didn't dress differently (that I noticed) so the faith came from knowing the other person or their history... it wouldn't have been an easy pack to join, but then being good at your job would earn you the same respect either way.