Over recent years it just seems you can show off by throwing money about, generally putting back a player's progress, and then selling at a big loss.
Bigger clubs tend to buy big and sell smaller, its the hazard of other clubs knowing you have money and the lower teams knowing you want something they have. Then using them up till the resale value is low.
Now this isn't a defence of our transfer policy, which has been shambolic for almost the Prem era, but the risks are higher and so are the prices.
Lets address the ones you listed
Johnson 17.5m- Was at the club 6yrs and was used as first choice RB for most of them, not a bad return really. The decline is more down to his attitude and ageing.
Carroll 35m- Yep we got done on that one, Newcastle knew we had the money and needed a striker fast.
Downing 20m- Overpaid, but the player failed to deliver, hardly the most consistent player even now at a club with lower expectations
Borini 10m- Rodgers fault, never worth the price and not good enough for the club and never will be.
Allen 15m- Another BR player for the dressing room.
Aqualini 17m- Came with a big reputation, the price looked good at first. Injuries, homesick and general lack of interest to play for the club
Of those, only Borini has been failed by the club and he shouldn't have been bought in the first place (discounting last summers buys as they've only had 1 season), the rest all failed themselves by not delivering their best.
But for those there is also Suarez, Torres and potentially Sterling. All bought for good fees, improved whilst at the club and sold on for mega bucks