Didn't you write some articles about it?

And since I get great tax write offs on properties, why would I buy treasuries?

The money spent on the flip will be a write off from your profit and shouldn't be taxed regardless. 

For example, the properties I held for many years have increased in value, have given me cash flow, tax write offs, etc. 

I have a hunch that you got some A I help in writing this!

What will be the cost of THAT money compared with the cost of a refinance of your current home at today's interest rates - taking into account that you will be able to write off the mortgage interest for a rental on your Schedule E once you turn it into a rental?

The 30-40k per year are written offers (not signed contract obviously but in writing nonetheless).

Here's a PARTIAL list:Office rentComputers, printers & softwareInternet & phone billOffice furnitureOffice supplies: paper, postage, ink, etc.Office liability insuranceAuto expenses: monthly payment, insurance, gas, maintenance, registration/plate feesBroker license fees: annual, monthly board & MLS fees, continuing education fees, E&O insuranceEquipment: lockboxes, signs, etc.Payroll & payroll taxesBusiness income tax preparation and paymentsLabor: answering phones, calling past due tenants, scheduling tours, taking marketing pics, processing those pics, writing ads, researching rent amounts, posting ads, explaining to owners how rent determined & showing where ad posted, opening & processing mail, posting payments, bank deposits, scanning documents & posting to owner & tenant portals, explaining accounting to owners so they understand their monthly statements, taking pics/videos of repairs, finding reputable handymen and contractors, confirming they're properly licensed & insured and tracking annually, verifying repairs done properly, processing invoices for utility bills, repairs, taxes, city inspections, scheduling periodic property evaluations/inspections with tenants that don't want strangers in their homes, explaining to owners why taking so long, and more & more & more...

I could write a book about Gatlinburg, the 2009-12 edition.  

Always have a contract in writing with GC.