A few thoughts:

1. Upgrading from Tiagra to Ultegra for Derailleurs, shifters, cranks, brakes will have zero impact on performance. Zero. Zilch. No difference. Perhaps enough weight difference that you can get a different reading on a scale, but not enough to be able to feel the difference while lifting or, even less so riding.

2. If you really feel your equipment is holding you back, the first thing that you should change (and the only thing that actually makes a difference in performance) is wheels and tires. get some lightweight, supple racing tires... high-quality tires - even on your stock wheels - will make the biggest gain in performance, and that is an easy one to get past your financial manager. Then get either some Shimano Ultegra pre-built wheels, or some other fancy aftermarket wheels (Zipp, Campagnolo, Mavic etc), or a set of Ultegra hubs laced to good quality rims (this would be my first choice). Any wheels that are compatible with your Tiagra 9sp cassette will work fine with Ultegra 10sp.

3. Does you wife ride? You could buy a frame and an Ultegra gruppo or parts kit under the guise of building her a bike to come riding with you, then put the Ultegra on your bike, and clean up and mount the Tiagra on her new frame.... IF you think she would like a road bike... if she would prefer casual rides on the MUP and rail-trails, get her the sweet $700 - $1000 hybrid of her choice. Even if you are not buying Ultegra parts and doing the ol' switcheroo, she will be more forgiving of spending on your hobby if it is something you share together.

Best of luck... to paraphrase from an old forwarded email... bicycles are superior to women because your bicycle doesn't care if you ride other bicycles