Well, being a '79 pace car makes it rare, being a 2.3turbo version makes it more rare. I doubt it was actually used on the track though, because the handful actually used at the speedway for track duty had Jack Roush built 302s under the hood with major upgrades that put them around 300hp.
New Car Prices, Used Car Values, New Car Reviews and Car Buying at NADA Guides has a section to help valuate classic cars, it may be able to help, but just because the book value is a certain number doesn't mean the current market will bear it. I just bought a '76 Mustang Ghia with a 302 and an automatic for $1000... 1/3 of it's book value, but last year I sold an '87 Mustang GT convertible for $3000... more than twice it's $1250 book value.
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1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4
tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)
Wondering the value of a 79 pace car 
