Need to start cycle-commuting – help!

Ok, so I’ve got a new contract that reduces my daily commute to just 8 miles each way. Helpfully, parking is £8 per day(!), so using the bike is definitely on the cards.

However:
I currently only have one bike.
I have never ridden to work before.

First thing’s first – the bike. I’ve got a carbon bike (think it was actually a Ribble originally, but stickered up differently by the shop) with SRAM Apex/Rival mix, Mavics and Speedplay pedals. If I ride this to work every day, then I figure that the Mavics will be taking quite a bit of abuse, and the speedplay cleats will wear out more quickly walking from the bike rack to the office etc. Plus, I like riding quickly and without mudguards/rack etc, so overall it doesn’t seem very suitable.

So, I’m feeling a second bike coming on. However, budget is limited to about £1k at the moment, so either:

Keep the current bike as it is, and buy something like a Genesis or Kinesis. I note the Croix de Fer is a couple of hundred over my budget. Also need to buy SPDs, shoes, rack and a smallish pannier.

Or:

Take off the Mavics, Speedplay, Fizik saddle, seatpost, Garmin mount etc. Replace with all the stock bits that came with the bike, put the lightweight plastic guards on (close clearances, no room for proper ones), buy SPDs, shoes, lightweight rack (the bike has no mounts – is this doable?) and use this as the commuter. I would then need to source a frame, groupset, bars and stem for under £1k including the bits added to the first bike. Plus, this would then be my ‘good’ bike, so I don’t know how achieveable this is.

Oh, and if anyone is thinking of suggesting that I buy something of theirs, I’m 5″11 and usually ride a 56cm (give or take for odd frame dimensions)!

Then as an aside, 8 miles doesn’t feel far enough to go to the trouble of putting lycra on (except maybe for taking a longer route home after work). Think I’d get away with just wearing work clothes with a hardshell jacket on?