I thought a bit about Loonook's math on the Lyre of Building.
Presume a sizable construction job, be it a church, warehouse, castle, or just about anything else involving massive amounts of labor.
First let's consider the human requirement. You need a DC 18 Perform check to make it work. A 2nd level Bard with a Charisma of 16 can get that with a Take 10. (Level +3 in skill, no bonus from the instrument, +3 from Charisma).
The user need not be a Bard, per se, just a performer with a total +8 in their skill check. Any class will do, including Commoner.
The Lyre costs 13,000 gp to purchase.
Presuming that half of your typical brick layers, stone masons and carpenters are skilled, and the other half are assistants who haul stone, lift support members and dig footings, and thus count as "unskilled", your average man-day costs 5 silver, 5 copper. (Based on the general estimate that skilled labors costs a gold a day and unskilled costs a silver.) Since the SRD version of the item doesn't include any restriction on skilled labor, and specifically mentions buildings, this is allowable.
Each half hour of play is the same as 300 man-days of labor. That means that an 8 hour day gives 4,800 man-days of labor. That comes out to 2,640 gold pieces worth of labor cost saved.
Dividing the cost of the Lyre (13,000) by the average day's cost savings (2,640), we see that the Lyre pays for itself in a shade under 5 days of use. (4.9424242)
Since it can be used only one day a week, that translates to 5 weeks. The down time isn't lost though, since it will probably take several days to haul in enough raw materials to supply 4,800 man-days worth of construction.
Let's presume that you're going to pay your "skilled labor" musician a full week's wage for each week (7 gold), even though they only work for one day. That's a whopping 35 gold, which is a bit less than the difference between 4.9424242 days and 5 days, in terms of labor costs.
So the Lyre and the lyricist are a very good investment for anyone doing any sort of large scale construction. Seriously, anyone in business would jump at the chance to make a capital investment that pays for itself in 5 weeks.
And any lyricist would jump at the chance fora job that pays a full week's wages for a single day's work. And though the possibility of a musician with a steady job and stable paycheck might fracture reality, it's one of those things reality will have to deal with.