It is a beautiful bright yellow bike. Who cares if it was a bottom of the line 10 speed? The weakest component on that bike is the SIMPLEX rear derailleur. Unless you're gonna ride in the rain, I wouldn't worry about the steel wheels. You have centerpull caliper brakes which if you were to install new fresh replacement KOOL-STOP salmon color brake pads should give you excellent braking except possibly during a heavy rainstorm. As for the SIMPLEX rear derailleur, yes it is inferior junk compared to anything from Shimano or Maeda SUNTOUR but hey if the SIMPLEX is in good shape and it probably is, will function reasonably acceptable for an inferior European rear derailleur. You can within thirty minutes install a SUNTOUR or SHIMANO rear derailleur if the SIMPLEX becomes problematic. A very simple and inexpensive upgrade should you need to do that. Keep it simple, why change everything if it does function adequately. Nothing is wrong with a 10 speed with friction shifting and adequate range of low to high gearing on the five of the freewheel. Hey, if the existing freewheel does not offer you the RANGE that you think you'd need, there are certainly thousands of used freewheels available with a RANGE that makes everyone happy. There are also still hundreds of NOS (new old stock) freewheels that might offer the RANGE you would want. The good news is that even NOS(new old stock) freewheels are relatively inexpensive! Used freewheels are next to nothing in cost. You can easily also find a used set of 27 x 1 1/4 (630mm twenty seven inch ...32-630) aluminum wheels from some mid seventies to mid eighties TEN or even TWELVE SPEED..................you don't need a top of the line donor bike from 1983 -1984 as even the bottom line offerings by that time featured aluminum 27 inch wheels........................Don't get caught up in the craze to change everything. Nothing is wrong with 27 (630mm) wheels, and you can still get tires from all the major online bike shops. Heck, that nice yellow bike that you have there has a cottered crank. After the rear derailleur, that would be the first thing to improve upon. I'd rather have a one piece Ashtabula American style crank than anything with a cotter crank because of the hassle associated with getting the cotter right. Again, if it ain't broke, don't fix it may apply here. The great news is that today it is almost really simple to change to a modern solution without cottered crank arms, and a superb cartridge bottom bracket. You didn't have that solution available in 1975. Good news again, that modern solution is relatively inexpensive if you source the parts and do the installation yourself. Don't get caught up in the idiotic craze to change everything and attempt to make it lose tremendous weight. Practical changes for enjoyable dependable riding is one thing but trying to change such an old bike into something it really can never be is just beyond silly. Make practical changes to make it enjoyable for you to ride. Nobody else matters! You aren't trying to impress the vintage Colnago, and classic Eddy Merckx riders. Save your money once you do that. You can always spend money on another cool bicycle for your collection...........classic-vintage "cool" or modern "cool"...............you are the judge so whatever you think is always right if it makes you happy & you have fun with it.
It is a great looking bike. That Yellow color is beautiful & classic and it can be seen from a mile away. Have fun with it. Just like with vintage automobiles, it doesn't have to be a Rolls Royce or a Ferrari to be a nice classic that people enjoy seeing today.