Yeah, the sprayer is awesome. Our hose is buried under waist-deep snow in the back yard, and danged if I'm going to go dig it out. But the quantity of crap that has melted all over the bike room is really gross (and really not worth even attempting to clean it up for another month or two) so it's nice to be able to leave more of it outside!
I think it's an oversimplification to say that expansion of the MBTA is the reason maintenance was neglected. Expansion is generally popular and there are lots of justifications for it, plus extra sources of funding, incentives, and so forth. The current expansion phase is actually still part of the Big Dig - promising to build extra transit is part of what gave the whole plan enough air-quality improvement "credit" to go ahead. The MBTA was also saddled with a whole bunch of debt resulting from cost overruns on other, unrelated parts of the Big Dig.
But the real reason is that we just haven't been willing to spend money on maintaining infrastructure. It's not just the T - we have tons of crumbling bridges, road surfaces that have gone way over the recommended maintenance interval, etc. We have potholes like you wouldn't believe. (There's one road on my way to work where there was a trolley that last ran in 1938, but the tracks (and the cobblestone street) are still under the pavement. I know they're still there because there are multiple eight-inch-deep holes where you can see them.) There are massive potholes on I-93 for that matter - and there is no way that fixing them costs more than the collective wear and tear on thousands of vehicles hitting them at 65mph every day.
Infrastructure maintenance isn't exciting or sexy, and it has no major interest groups or lobbyists except maybe construction unions. No one puts on big demonstrations, marches, ice bucket challenges, walk-a-thon's, etc, for shoring up retaining walls and inspecting overpasses. No congressional representative gets on television for saying they're going to raise taxes to fund a round of road construction or bridge safety evaluations or buy new snow removal equipment that will be needed only every 5 years (but needed desperately then). It's just one of those things that goes to pot slowly enough that you kinda don't notice, until a disaster happens and everyone wrings their hands and acts shocked that we could have let it happen.