Let's take a perfectly good, classic sports car like a 1987 Lotus Excel SE.

The front of the car is beautiful - which is why it features prominently on many profiles.

But the rear is a challenge. It lacks the same style.
Can we do something about that?

The spoiler is very large and appears to be an after thought.

Apparently, the Excel originally had quite a small rear spoiler:

" In the mid 80's to sell a car with performance appeal you had to have a bigger spoiler on the back.
Ford XR3i's to Porsche 911's had big spoilers.
So Lotus increased the size at the back, then to restore the handling they had to put
a deeper spoiler at the front also; the result - a slower car"
View the original thread at Lotus Forum

THIS IS A RADICAL APPROACH:

View the full project by clicking here

Below is the later-model spoiler refitted to the car.
Looks like a waiter's tray.
This is how it was originally.

It has now had 50mm ground off the bottom and is shown being
glued (epoxy resin with filler powders) to the boot lid as a first step.

This lowers the profile to a manageable shape.

The next step was to fill the gap, seen generally as a shadow beneath the spoiler.

It may not be obvious in this photo but the body line now flows over the top of the spoiler,
around the gentle curve and down along the boot face.

The batteries shown on the lid are holding a piece of plywood in place, that now fills
the top cavity, while the epoxy resin hardens there as well.
This cavity will be faired off.

The spoiler outside edges need to be faired to follow the body line,
and that should be pretty much it.
A weekend's job, apart from painting.

More in keeping, but there's more to do - the indent under the tray is ungainly.

This shows the underside of the tray being filled, so that
the body of the car flows up the side of the rear guard, and
curls into the top tray. The corner follows the line of the car.

The second image below shows how a mock flare is being blended
into the top piece, under the window. The lighting is deceptive - there
is no sudden cutoff along the ledge. That is not shadow, it's dark body filler.
The result will be best seen when the boot assembly is painted.

However, the ledge does need to be built out, to curve,
to follow the top line

With a gentle curve now:
primed, with some pink and white body filler
yet to be sanded down

(2008 Update)
Let's add a spoiler:

Now, let's take a look at the rear guards:
Glue foam filler.

Apply lots of epoxy filler.

Sand and shape and sand and shape

Back..... Let's fit a Supercharger