Wondering if electrician is scamming me on panel replacement
He condemned a QO panel... Without even opening it??

QO is Square D's top line industrial grade panel, and it's current stuff.  The way panel pricing works, you can get the industrial grade for just a few dollars more.  (Square D also sells a residential grade line called literally Homeline, it is acceptable also, but QO is excellent).  

So he's just wrong.  And chasing dollars obviously.  More disturbing... he didn't open with obvious defects in the location of the panel - or to be more precise, remodeling done around the panel.  The original electrical work was well-done, but then somebody decided to "finish" the space, and disregarded the electrical codes, probably because they were a carpenter. 

One wonders if the work was permitted, since what AHJ would permit a clothes closet being placed in front of an electrical panel? 

The closet needs to be demolished (or at least truncated) so there is a work zone in front of the panel.  It must be 30" wide (the panel can be to the left or right side of that 30") and 36" deep so the electrician can stand at arm's length. It must have at least a 6' ceiling so a fella can stand.  And you must keep it clear of stored junk.  

This is a $500 carpenter job, not a $4500 electrician job. Unless the closet is sacred for some reason; did George Washington hang his coat there? Maybe he hung his coat in the left side of the closet. 

Aluminum

I'm sure the electrician told you a lot more than that... But the aluminum thing is what stuck.  There was a problem in the 1970s with shoddy use of aluminum wire with receptacles (wire terminations/clamps) that had not been properly approved for aluminum, and this resulted in a lot of arc problems which led to house fires.  Easily fixed with arc-fault breakers, but there is still an ooga-booga fear, moral panic style, where any aluminum wire of any kind is consided "cootie".  Certainly a shoddy electrician could scare you into doing unnecessary work by mentioning the A-word.   

The aluminum excuse is balderdash.   Actually service and feeders are aluminum for good reason, and aluminum performs just fine in these large wire sizes.  So you want lugs to be aluminum, since aluminum lugs are the universal donor - they work with Aluminum and Copper both.  Copper lugs don't play nice with aluminum wire (and actually, that was the problem all along).

Even today, aluminum is not used for small branch circuits (lights, sockets, dryer etc.) because of the cootie. The alloy has been improved, the now-noncopper terminations have been vastly improved, and it's legal... Just nobody does it. 



Now on panels, here are brands I would consider solid and not even think about replacing: 


Eaton / Cutler Hammer CH (Cutler Hammer) or BR (BRyant). 
Square D QO or Homeline.
Siemens/Murray
General Electric
Challenger, but only the panel.  Challenger breakers are bad and should all be changed for BR breakers, which properly fit owing to a past relationship with Bryant.


Zinsco, Stab-Lok and Federal Pacific (in US) are dangerous and must be ripped out.   Pushmatic is a fine panel, just obsolete. 

If it were me...

The undiscussed problem here is that your panel is full/overfull.  It looks like you have plenty of service, but are using "double stuff" breakers to get enough circuits.  

Here on SE, we love large panels.  Because many circuits today need AFCI or GFCI protection, and those breakers are not available in double-stuff.  What's more, it's very frustrating to not be able to install something new, like an EV charger or hot tub, because of a full panel.   

So. That's a 30-space panel, looks like the standard size that fits between 16" joists.  I would get another one as a subpanel - also 30 space, also QO, but main-lug (no main breaker).  Fit it in the next joist bay over so it fits in the same 30" wide electrician's work space.  Move 2-4 circuits over to the new subpanel to make space, then fit a 100A breaker in the main to feed the subpanel.  

You'll have 58 total spaces, which is a very happy number for a medium/large well-equipped house.  

Now you can add anything you please without concern.  And if a couple bus bars actually are arced up, just stop using them - leave the arced breakers in place connected to nothing and move the wires to new breakers.