OK, the first thing is that if you think you need to lie about this kind of stuff, your marriage is in deep trouble already and before you think about getting even a set of strings you'd better work out that vital issue first. Second, I'd advise the OP to sit down with his wife and spend a lot of time coming up with a shared financial plan that covers both long-term and short-term goals.
Third, don't covet your neighbors' gear. What He has for you is for you, which also means what He has for me is for me, not you. OK, so why do I have two US Laklands, a Skyline, a Fullerton-era Vintage Series '62 P (in the rare Lake Placid Blue no less), etc. etc.? Because...
1. I managed a guitar store from '77 - '88. Didn't make much money and should have left it about five years earlier than I did. But that's in the past and I can't change THAT boneheaded financial move! And I did acquire some good stuff then, and I learned to be able to know exactly what I want and not waste money on settling for something less, trying to modify it to meet my needs/wants, and the trying to flip it so I could buy something else.
2. I gigged steady from '76- 2002, and made good money at it. But more importantly I ran the business side like a business. That means (among other things) I reported every dime of the income, but also took every legitimate deduction I could. And for a good long while there, the tax implications were that I either buy new gear or I pay taxes on the income. In retrospect it may have been more wise in the long-run to have paid some taxes and used the income for other things than music (I came to "Dave Ramsey land" very late in life), but again, that's done. Bottom line is I have those instruments because I acquired them over 30+ years of gigging and working in retail music. The Fullerton-era P bass was just a brand-new bass when I bought it in '83 for $500.
3. I don't have stuff I can't use. OK, I do have stuff I don't use, but that's because I'm not gigging now. But I don't have any use for one, let alone two 8x10 cabinets. I'd LOVE to have a great Jazz bass or clone, but there's no reason to justify it now. That's part of the "what He has for me is for me" thing. Read Psalm 23 carefully (I feel safe in that because you've said your gigs are church gigs)- that first line says "... I will not want". Don't assume that only means that you will not be in need, but also that you will have what you really need. It comes to the discussion of "need versus want" that you and your wife need to frankly discuss over time in your financial planning discussions. This stuff needs to be talked about together, so don't abdicate your responsibility in financial planning, nor put the blame all on her.
In summation...
Talk about it
Be patient
KNOW what you need and not merely justify
Trust (Hebrews 11:1)
John