I had a Grand Prix made in 1973. My biking friend had one made in about 1970. His was made in England (Carlton?). Mine was made in Belgium, as the Raleigh workers were on strike. It was a decent bike (this means a good bike). We used our Grand Prix's for everything from racing, touring and even cycle camping with bags.

This was the first bike that actually fit me. It had a relatively soft ride. I went through the upgrading process and when I was done it really was a good bike. I installed :

Brooks B-17 saddle,
Campagnolo seat post (25.0 mm diameter post plus a shim to fit the frame),
Sugino Mighty Comp crank set (this really made a big difference but I'm not really sure why)
Light weight aluminum rims and light weight, low profile clincher tires (I reused the hubs),

Of these, the wheels/tires were the most important upgrade. The seat post saddle meant it was comfortable to ride. The crank repalced those horrible cottered, steel cranks.

You could do these upgrades at relatively low cost if you buy used parts on ebay. Look for Shimano and Sugino instead of Campagnolo and you will get what you need at very low cost.

This lasted me about 2-3 years until I bought "Bob".