Continuous path of elements satisfying a condition

I have input like this:

<root>
	<item id="1">
		<item id="2">
			<item id="3"/>
			<item/>
		</item>
		<item>
			<item/>
		</item>
		<item id="4"/>
	</item>
	<item>
		<item/>
	</item>
</root>

I am only interested in item elements that have id attributes and form a continuous chain
from the child of the root element to a leaf.

1) I can select the leaves and then all the relevant items with

<xsl:variable name="leaves" select="//item[@id and not(*) and not (ancestor::item[not(@id)])]"/>
<xsl:variable name="items" select="$leaves | $leaves/ancestor::item"/>

Is there a better way?

2) In the template for an item, I need to loop through the item's children that meet the
conditions (i.e., that are in $items).  I've tried this

<xsl:variable name="nitems" select="count($items)"/>

<xsl:template match="/">
<xsl:apply-templates select="$items"/>
</xsl:template>

<xsl:template match="item">
<xsl:for-each select="item[count(. | $items) = $nitems]">
	...
</xsl:text>
</xsl:for-each>
</xsl:template>

This is fairly elegant but testing in my environment (MSXML) shows it to take 4 seconds
while a recursive template that just sums the number of included items that are 
children of the current item runs about 50 lines but takes half the time to run.

Thanks,
Chris