Having a ride closed for a year for no reason makes people complain but if there was actual observable work happening, people would be more understanding and, more importantly, more likely to come back to see what's happened to it.
Out of interest, what work are you suggesting on the wooden coasters during this closure? Retracking an entire coaster at once (as some people have suggested) would be pointless as newer sections do not need retracking yet - it would also be a huge financial outlay for the park with little return, as well as the negative impact on the park as already mentioned.
The amount of re-tracking and repairs, the kind that need the track to be held down with clamps and not the kind due to salt, that have been needed on the Big One shows just how much of shoddy job it was. Look at how much they had to adjust the turnaround by!
The turnaround (and first drop) were profiled badly by Arrow initially, but that was rectified. This has been the case with lots of rides over the years, even much newer ones which have required tinkering over the years (Smiler's track not lining up during construction comes to mind as an example).
The problem with the pleasure beach, for me, is that it's stagnating and has done for a while. Mandy has done a great job with the hand she was dealt. She's smartened the place up and made it look inviting and somewhere posh instead of the seaside fair it was. But the ride line-up has remained about the same for years, they really need to improve the rides they've got and get some new ones in. Project 2018 will be make or break for them I think and it's unfortunate that it now lines up with Alton's next big investment, we could be seeing another 1994.
I know someone is going to say something about Nick Land and Wallace & Gromit, and they'd be right. Nick Land was a nice refresh of a tired looking Beaver Creek, but Wallace & Gromit was a step back for me, it's far too bland in between the scenes and needs something else, I guess this where the hand-wavy word "charm" comes in, that Goldmine had.
I disagree that the ride lineup has remained the same. Over the past few years, BPB has opened Nickelodeon Land (£10 million investment) which included 6 new rides, Wallace and Gromit (regardless of your opinion on it, it was a new/heavily refurbished attraction) and Skyforce. Whilst this isn't what everyone wanted to see at the park, it is investment nevertheless.
As well as this, they have spent a lot of money refurbishing several areas and rides; Revolution had a completely new colour scheme, Steeplechase had a track repaint and refurbished station, Valhalla had its entire frontage replaced and updated scenes, new flooring was added around the park as well as several other repaints (not all for the better!) and considerable cosmetic work - something which a lot of other parks fail to carry out.
I don't understand this obsession with classic rides? The Grand National is painfully "boisterous, rough, throw-about-y or whatever word you wish to use-y", and the trains on it are destroying the track making it worse every season. Imagine a nice roll in place of the Valentines hill! Imagine the speed it could carry with proper trains and track! The Big Dipper is just boring. If these rides are in the way of progress, get rid. They do nothing that warrants special treatment. Memorialise them if you must but history shouldn't get in the way of the future.
The classic rides are fantastic examples of the rides that paved the way towards the rides you see being built today. They are unique assets to the park and set it apart from anywhere in the UK if not the world - removing them would be taking out the very thing that makes BPB special. Not to mention the fact that they are very fun coasters, but of course they split opinions as any coaster does - if you don't like them, that's fair enough - personally I don't like Rita at Alton, but I'm not calling out for it to be torn down as plenty of people do enjoy it!
I do agree that the National needs different trains (the old ones back would be ideal), but the layout should stay the same.
Regarding your point about the historical rides standing in the way of progress, several of the older rides have already been removed in the name of progress (or in some cases just removed), so I think that the park has reached a stage where it can develop as a fully functioning theme/amusement park whilst retaining the bulk of historical rides to run alongside new additions.