Relink from One Image File Type to Another
Eugene asked an excellent question in the comments to this old post:
Say if I do decide to change the .tif to .psd and I move the .tifs out to another folder, would it or would it not be a good idea if Indesign said, "Hey, those .tifs aren't available, there's a similar name with a .psd extension, would you like to use these instead?" Then you just press, yes use my .psd files.
Many folks had asked for this ability, and so Adobe delivered: InDesign CS4 has a feature called Relink to Folder. It's an awesome command (it lives in the LInks panel menu) because it basically directs InDesign to some other folder on your computer (or server, or whatever), where your images may live. So you can relink a hundred images from one folder to another quickly.
But even cooler, you can tell InDesign whether to insist on the same file type or use a different one. Here's the control in the Relink to Folder dialog box:
So, you select one or more images in the Links panel, choose Relink to Folder, tell it which folder to look in, and choose a file extension. The original image doesn't even have to be "Missing"! In fact, the two images (psd and tiff, in your case) can even live in the same folder.