I've just bought a Synapse (carbon) and it's my second bike since going back to cycling in late 2014 after 20-odd years as a Basketball player. Injury forced the change and the first bike I bought was a Rose DX2000 Cross bike (slightly over your budget but great value). That's an aluminium cross frame with 46/36 chainring and yet I did both the Tour of Cambridgeshire and PrudentialRide100 on it in 2015 with a 29km/h and 27km/h average respectively. I have a set of road wheels and cross wheels so have just swapped as and when. I've enjoyed my riding on it so just shows you don't need to overly obsess on a 'race', 'sportive' or 'gravel' bike. Most bikes can do most things.
It took me that long to get an idea of what I wanted from a bike as well as being able to choose a frame that would fit me. I got myself fitted on the Rose last March and used the data (particularly stack and reach) to buy the Synapse. The Rose came with disc (mechanical) and 10spd 105, which I believe is now equivalent to this year's Tiagra. The Synapse is also a disc bike (Sram Red HydroR). I like disc brakes and wouldn't buy a bike without them as they fit what I use the bike for. Cross off-road through Epping Forest and surrounding bridleways/towpaths on the Rose and long(ish) and steady(ish) rides on the Synapse plus sportive (this year's Velothon Wales, ToC and RideLondon100). I like a comfortable position so chose an endurance model. I narrowed my choice using my fit data, something you haven't got, so Ollie's advice is spot on, try the bike if you can. I notice you are looking at a Specialized Allez, why not the Roubaix? Finally, if you're looking to stretch your budget, a look at online retailers Rose or Canyon might be worth having.
Whatever you chose, get it fitted properly and just enjoy riding it. When I bought my Rose, within 12 months the equivalent groupset had gained a cog at the rear and hydraulic brake operation, things move so fast there's no pleasure trying to keep up!
Oh, and ability-wise, I'm 1m89 and 110kgs and I chose the club as it is so welcoming. I have cycled with members on organised rides and on the track and have never felt out of place. Very welcoming, so much so that I cycle an extra 30kms to and from home in Woodford to attend the weekly ride, when I do.