When I was young, I raced road bicycles in Central Queensland. My racing bike had pedals with toe clips. In those days, the only clipless pedals and shoes were Look pedals – and they were extremely expensive. These days, clipless pedals and shoes are a lot more common and available at affordable prices.
When I bought my Fuji flat bar road bike, it came with Wellgo Lu-948 pedals with MT-14 toeclips fitted – within a couple of days, the right-side pedal squeaked terribly. Rather than pursuing a fix under warranty, I replaced the pedals with clipless pedals.
I purchased Shimano PD-R540 SPD SL clipless sport pedals and a set of dhb R1 road cycling shoes. Value for money, the dhb R1 shoes are quite okay. But I love the Shimano pedals. They are so easy to clip in and out of, but also give a lot more power going up hills and accelerating hard. However, I do find them a little hard to get back into quickly at traffic lights sometimes.
In my opinion, fitting clipless pedals is one of the best, and easiest modifications you can make to a bike.
My next modification will be to put on some narrower rubber when my current tyres wear out. I have a Vittoria Rubino Pro 700 x 25C tyre waiting for the original rear tyre to wear out and will probably put the same on the front wheel. After that, perhaps a close ratio cassette, and a pair of lighter wheels?
Even in its current near standard spec the Fuji Absolute 3.0 is quite fast. In fact, I quite regularly pass riders who are 20 years younger and 20 kilograms lighter riding racing bikes and wearing all the lycra gear. They must feel a little embarrassed having a fat old guy passing them on a flat bar roadie!