At the end of the day it depends on what you are going to do with the bike. Every so often the goal posts move with regards to kit (basically what was Sora becomes Claris etc.) so the levels are always getting better. Once you are off the bottom of the rung you're going to get a bike that would knock spots off of its equivalent 10 years ago. I'm presuming events are sportives? Then you want to consider number of gears and ratios. Look at the cranks, a triple gives you options that a compact (double with 50/34 teeth on the rings) doesn't, although you may find it ends up redundant, a compact gives you less at the beginning, but when it's sufficient allows you to use what you have better (you shouldn't go smallest ring on a triple to smallest cog on the cassette for instance). When you've decided on crank, look at the gearing on the cassette, the small number is speed, you probably want it to be an 11 or 12, the largest is hill climbing, 28+ would be handy. Consider that the more gears you have, the more granularity you have between the biggest and the smallest, which can make riding smoothly easier. Again if you're not doing larger distances that's not an issue, if you are looking at cycling 15-20 miles plus then it's probably going to be a factor.
Also, have a think about the brakes, what you want, what the options are, and make sure you are comparing like for like throughout the kit, you can find that sometimes the cheaper areas get better levels of kit but the more expensive bits are 'scrimped' on (so Tiagra derailleur but Sora shifters).
Finally, there is a cut off point with cycle to work (around £350 I think) where the tax break changes so you save less money. If you decide you are down that end of the scale, it may become a factor.
Oh, and cost up locks etc. at the same time. If you have nothing, it's not just the bike you need. Rule of thumb, 10% of the value on locks.