I'll get back to you on Eurostar staffing levels in two weeks;-)
A one-way WAS-NYP ticket in First on the Acela is $319-455 for tomorrow (and most of those tickets are either at $420 or $455). The $319 fare is just above the full-flex Business ticket ($309) but only shows for one train, and that train shows a $173 "normal" Business ticket. So basically, you're looking at "Business plus $146" for First.
On paper, that's up to an extra $6424 in revenue.
As to the economics, a few things should be noted:
(1) The economics in 2018 are not what they were in 2003.
(2) Similarly, the economics of six-car Acelas on hourly frequencies right now does not necessarily apply to the situation that will exist with the Acela II.
(3) There is an intangible goodwill value to a comped-up First ticket that can plausibly attract repeat business elsewhere.
(4) Finally, First and Business pax are not 100% interchangable. There are at least some higher-dollar passengers that either want or need the benefits of First (a hot meal, single seating, etc.) who might not take a seat in Business.
At the low end, WAS-NYP a First ticket represents a markup of just over 84% to the corresponding Business fare ($173 vs $319). At the high end, it represents a markup of just over 47%. This would seem to more than cover the "cost" of lost seats at the high end (44 vs 65): At the low end, the First fare "should" be $255 (148% of $173). At the high end, it "should" be $456 (vs. $455 as charged).
So, let's check those buckets and then play a game...
Code:
Business First I-First Difference
$173 $319 $256 $63
$204 $350 $301 $49
$234 $380 $346 $34
$274 $420 $405 $15
$309 $455 $456 -$1
I-First is the implied First fare based on lost seating.
In a theoretically sold-out coach with seats distributed evenly across the buckets, First generates somewhere in the ballpark of $1400-1500 in excess revenue versus a similarly-priced Business Class car. I say "in the ballpark of" because one can generally not price eight tenths of a seat at a given price. I suspect the dynamics are more complicated than this, but at least we have a hint here. That $1400+ should make up for lost F&B revenue and then some. If we were to burden the First attendants' cost to $50/hour (wages, benefits, etc.) that would generate a cash cost of $300 for the trip (for two attendants). That gives about $1100 in net revenue less actual F&B and any "lost" F&B sales.
I cannot speak to the actual catered costs for the meals, etc. But it seems at least plausible that $1100 would be enough to cover those costs. And please note that I have analyzed WAS-NYP here. WAS-PHL shows an upcharge of $103 while PHL-NYP shows an upcharge of $92, with similar proportional pricing dynamics. So in reality there might be a bit more slack (in raw dollar terms) to work with, though that would come with some added F&B costs (though no increase in OBS expense, to be fair). And all of this is before any discounts (which would *improve* First's relative performance, since those don't apply to the accommodation charges but they reduce the base fare, and thus the implied First fare). My guess is that a peak-hour, packed First car runs a good chance of generating about an extra $1400-1500 net of the OBS expenses on the WAS-NYP run.
Sliding back around, if we presume that the First car is a "break-even" proposition over another Business car in pure revenue terms, it does provide several avenues to induce ridership, ranging from elites getting to bump up (this is a good part of my incentive to keep grabbing Select Executive) to picking up another segment of the market. And again, don't forget that in plenty of cases Business seats aren't selling out but First seats are selling, so it *is* a bit of a fallacy to treat a First car as a totally interchangable option vis-a-vis another Business car from a revenue perspective.
So he can give you amazing insight on this particular topic. 
