Question: How many bikes does a roadie need to have?

Answer:  One more than he/she currently has. 
That seems to be about right.  I think I may be close to having enough bikes.  It took about 6 years, but I may be content with owning 7 bikes... each with a very specific purpose... I need each one.

My garage is set-up nicely to house my collection of two-wheeled vehicles.

1) Commuter Bike - this is an old 1988 Trek 1000... I put a saddle with flames on it, and cheesy yellow tires in hopes of making it less theft-prone...  the down-tube shifting is ridiculous... really a single speed because I don't like shifting old-school, too much grinding... the gears were weird back then... cyclists must have been stronger, because I ride in the small ring, the big ring is too large, I guess...  I think it is a 6-speed... I need to commute more...

2) Mountain Bike - Nothing fancy... Marin hard-tail with front shocks... had it about 10 years... still works fine... I take it up to sugar bottom about twice per year, and also haul my son with it...

3) Cyclo-cross  Bike - I bought a Giant CX bike about 5 years ago for $600... still in excellent condition and I use it for gravel training and the occasional race or gravel brevet...

4) Training Bike (Indoors) - My first race bike (Trek Madone 5.0)  has been demoted over the years, and has now been relegated to its final resting place in my basement.  I ride it all the time, as I am sort of a fan of indoor training.

5) Time Trial Bike - My Trek Equinox is getting a bit outdated, and was mid-level when I bought it, but still does the trick... I have a good areo-wheel/handlebar set-up to compensate for the shimano 105 components that came with it...  I like the fact that it isn't the 'latest/greatest' because then I can blame my equipment if I don't do well in a TT or prologue.

6) Training Bike (Outdoors) - Ok, this is my previous racing bike... I didn't even think about selling it, as it comes in handy for solo training rides,  rainy group training rides and/or recreational rides that don't imply my 'race bike'.

My new bike is still awaiting its 'maiden voyage'...

7) Racing Bike - My new Trek Madone is for racing and group race-simulation training rides.  I haven't ridden it yet... 

Along these lines, I have a three car garage, and only one-car... that seems like more than enough... I like the idea of having 2/3 of my garage dedicated to my bikes.

So, I am sort of at 'critical mass'... in that if I get another bike, it will be to upgrade one of my existing bikes, and I will have to finally part ways with a bike.  Hmm, I suppose if I get a girlfriend/wife, I might need to get a tandem... that seems like a hassle.. I will stick with the current plan which is "to nut-up and die alone".

So, the answer to the question, in my opinion is 'SEVEN'.